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Planetary Assault Operations: A White Paper

This article was originally posted to the website in 2000, and appeared in this form in the May/June 2017 issue.


There are a number of references to planetary sieges and the taking/retaking of planets by opposing navies in the Traveller Canon, especially during the Frontier Wars. And while the Imperium mainly controls the space between the stars, there are times when the enemy isn’t only in space. And while a hostile planet can be interdicted, bombed, and talked to from orbit, only troops on the ground can truly control it. This is my attempt to explain how I think a planetary assault would work and how one could be set up in a campaign as background, plot device, or adventure. I have also included a brief glossary of terms at the end of the paper.

Assumptions and Givens

  1. This is my opinion; your game setting may well be different and this material of limited applicability. Much of this is based upon my knowledge of airborne operation as a former member of a U.S. Army Airborne unit (the 519th Military Intelligence Battalion (Tactical Exploitation) (Airborne), where I worked with [Freelance Traveller author] John Groth).
  2. I am using the Third Imperium from about the time of the Fifth Frontier War as a baseline for the assaulting force; this implies an average TL-13 with a top TL-15. Switching this to other races should be relatively simple and I will include some notes.
  3. I primarily play and referee Classic Traveller, but I will include references to other milieux. I hope to keep this as generic as possible.
  4. I am assuming that the Imperial Army will undertake large-scale planetary actions. I view Imperial Marines as ‘johnny-on-the-spot’; they are the visible might of the Imperium and deal with brush fires. In large-scale actions they will concentrate on ‘traditional’ marine roles—boarding actions and quick assaults. With ‘organic’ support (artillery, medical units, etc.) and heavy units the Imperial Army and its colonial units are going to be the major players in ground actions. [Editor’s note: For those unfamiliar with the term, the military use of ‘organic’ in this context means that it is part of the unit, or of the same parent unit, rather than supplied by an independent unit.]
  5. The relative superiority of near-space by the navy of the attacking force is a given. Without close orbit superiority planetary assaults are effectively doomed. This does not mean that the attacker must absolutely control close orbit, just that they must be capable of projecting great force into near orbit at specific times.
  6. Specific tactics will vary based upon the tech level of the planetary forces. Against foes of TL-0 through TL-5 or so the Marines just set down in grav vehicles and move out. While a large TL-5 army with heavy support could actually mount a credible defense against TL-15 marines in battle dress, they will not prevail. At higher tech levels, however, you can face serious opposition as those large armies gain nuclear weapons and more sophisticated armor and aircraft. I have divided assault procedures into TL-6 through TL-10 and TL-10+.
  7. I am taking it as a given is that military forces will generally be smaller as tech level increases. This will, of course, vary based upon law level, political stability, war footing, etc. But just as many modern armies are smaller than they were in previous generations, I am assuming that the increased efficiency of higher tech levels will reduce the number of sophonts under arms.
  8. This all assumes that the attacking force actually wants to capture the planet mostly intact. If there is no interest in preserving the structures, resources, or population, I assume that a heavy orbital bombardment until the defenders were unable to resist would be sufficient.

Planetary Assaults


A clear military objective is the key to clear military success. The ultimate goal of a planetary assault is to control the planet. In order to do this, the military objectives should be (not necessarily in order):

  1. Render defending military forces unable to effectively resist (‘combat ineffective’).
  2. Control or neutralize the defender's governmental or administrative functions.
  3. Control or contain major population centers.
  4. Secure means of resupply/reinforcement of attacking/occupying force.


Initially naval forces will conduct ortillery [‘orbital artillery’—ed.] attacks against strategic targets. Defensive emplacements, command and control centers, sensor clusters, military bases, and downports will be primary targets. It is also highly likely that general infrastructure will be targeted to reduce the enemy’s will to resist. Civil engineering (dams, mass transit, etc.) will be targeted. Depending on the level of resistance and the volume of ortillery fire available it is possible to reduce a planetary population to using flashlights and shipping water in trucks in a week. The initial phase of ground assault is usually the use of drop troops (also called jump troops). Inserted from orbit, drop troops rely upon surprise, speed, and violence to secure a landing zone (‘LZ’). Once secured, the landing zone is used to land heavy weapons, grav vehicles, landing ships, etc., etc. A secured LZ is called an ‘orbit head’. The orbit head(s) are the start points for ground attacks against defenders and can quickly transform into the equivalent of a class C starport. The main ground assault is performed by a mix of light and heavy infantry, mechanized infantry (infantry and g-carriers), armor, artillery, and support units. Because of the mix of units the force as a whole is called a ‘combined arms army’ or just ‘combarm’. Assuming the ground assault is successful, there are follow-on units that help secure the planet. Ranging from psychological warfare units to military journalists, these units strive to replace the destroyed or removed infrastructure and government of the planet with the tools of the Imperium.


Although it may be unusual to think of an operation as large as attacking a planet as tactical, but to a military force capable of such an action it is. The most critical decision is; where to insert drop troops? While this should remain fluid to allow changes based upon the differences from one operation to the next, it is often very advantageous to insert an orbit head near a population center of the defenders. In addition to allowing the operation to immediately threaten defenders, it will reduce the ability of the defending military to respond with full force without endangering their own populace. The simultaneous insertion of multiple orbit heads is also preferred. This will force the defenders to split their forces and the attention of their command staff. The use of deadfall ordnance at the same time can add confusion since gravity bombs can easily be configured to produce the same sensor imagery as drop pods.

Drop Troop Insertion

The most critical period of planetary assault is the insertion of drop troops. Although supported by orbital fire the drop troops are very exposed to defenders and can suffer significant losses before reaching the ground. To increase their chances of securing an orbit head they are accompanied by a number of tools configured to resemble troop pods to sensors. The first such tools are ‘Landing Zone Preparation Devices’, also known as ‘daisy cutters’ or ‘Sylean scythes’. These explosive devices are the first pods fired and are designed to mimic troop pods. About one third of these devices detonate about the LZ and use gravity lensed explosives to direct a concussive cone toward the surface. The massive overpressure is designed to detonate any mines in the LZ and knock down most plant life and structures. The remaining devices detonate on impact and are grav-focused to concentrate their force in a 3-meter high plane parallel to the surface, flattening any remaining foliage and obstacles. The most common devices that drop amongst the troops are jammers. In addition to radio and radar jammers, there are also meaconers (devices that distort navigation signals, i.e., give false GPS results), repeaters (devices that record defenders’ radio communications and repeat them over on over on a number of frequencies), and mimics (devices that send electronic and radar ‘chatter’ that resembles the defender’s communications but give false data). Also accompanying the drop pods on the outer fringes are defense pods. These grav-stabilized devices have radar/lidar sensors and a laser cannon, all powered by a fusion generator. These air defense systems are designed to shoot down enemy aerospace fighters, missiles, etc. Once they are on the planetary surface they will continue in this role until out of power or shut down by the drop troops. Last but not least, each squad will have an equipment pod. The equipment will vary based upon each squad's particular mission, but will include heavy weapons, air defense systems, telecomm gear, and combat engineering tools.

Tech Levels 6 through 10


While never easy, planetary assaults against worlds at tech levels 6 through 10 are less difficult. Defending forces do not have access to meson weapons or powered battle dress. Also, the heavier man-portable weapons are not found at these tech levels. As mentioned above, however, a large force with the support of nuclear weapons can mount a stiff resistance. The attackers must be sure that orbiting ships can provide nuclear damper support until the drop troop can set up their own. The drop troops themselves will be optimized to repel a large number of attackers with little special attention to heavy weapons. The average trooper in battle dress with an FGMP can deal with a great many main battle tanks of a TL-8 army, after all. The defenders will also have less sophisticated sensors, making deception more effective. Combined, these make it likely that there will be more deadfall ordnance attacks and fewer actual orbit heads (no more than one per continent, likely only one or two).

Tech Levels 11 and higher


When the defenders approach or equal the technical ability of the attacker the risks become greater. The inherent advantage possessed by the defenders forces the attackers to take greater risks. The high mobility and concentrated firepower of high-tech forces almost compels the attacker to try and overwhelm defenses with the number of attacks. The best option for the attacker is to release a near-flurry of troop drops and deadfall attacks combined with heavy ortillery barrages. Preparatory ortillery must especially focus on meson sites and aerospace fighter bases. The drop troops must be prepared to face a number of threats, including grav armor and meson gun artillery.

Special Note

The use of nuclear weapons to generate an electromagnetic pulse (EMP) effect is very common during planetary assaults. Against TL-6 through 10 defenders this can be a devastating attack. And the effect against high tech opponents can be more severe than may be assumed. Although most TL-11+ electronics (especially military electronics) are shielded against EMP effects it will still temporarily overload most sensors, increasing the survivability of drop troops as they enter the atmosphere. Also, while civilian communications systems may be shielded, often their antennae are not. While the means of communication will remain intact after an EMP attack, large areas of communications blackout will exist until antennae are replaced. This will add to the fear and confusion of the defenders.

Support Operations


Intelligence preparation can be a critical force multiplier in planetary assaults, especially against high tech level defenses. In addition to the routine strategic intelligence gathered by Imperial Intelligence, a planetary assault requires an in depth analysis of tactical response measures, apparent willingness of defenders to endanger their own populace, and overall readiness of the defenders ground forces. Effective counter-intelligence operations can also increase the levels of tactical and strategic surprise of the attacking force.


Commando operations in support of a planetary assault are extremely dangerous and prone to failure. However, when they are successful they can have a considerable impact upon the defender’s will and ability to fight. For these reasons, they are often popular with players. If strategic surprise can be obtained commandos can be infiltrated and supplied in a large number of ways. Their initial targets will generally be command and control, telecommunications, and strategic defense systems. The following scenario is a demonstration of the potential impact of successful commando operations in support of planetary assault: Three commando squads are infiltrated onto a TL-13 world in advance of a planetary assault. Arriving as workers, tourists, and ship crew, they are supplied with a full combat load, including battle dress, smuggled in by intelligence operatives. In a coordinated series of attacks, two major telecomm hubs are sabotaged by pre-set explosives, a similar attack damages the refueling facilities of the major aerospace defense center, and teams of commandos in battledress armed with FGMPs assault the members of the planetary government, planetary defense commanders, and a deep meson site that defends a section of the planet. During the resulting confusion reports are received that an enemy fleet has jumped in-system and is on vector for planetary orbit. In addition to potentially neutralizing the defender’s civil and military commanders and seriously disrupting planetary defenses these actions could very well panic the defenders, degrading their ability to fight.


While the first step is getting troops on the ground, the key to winning is supplying and reinforcing those troops. As soon as the orbit head is secured the follow on forces must begin to arrive. Initially these forces will be as ‘heavy’ as possible, i.e., g-carriers, grav tanks, and artillery pieces, preferably in large landing ships. This will be followed by a mix of combat and support units.


The job of the Navy is not over once the troop pods are fired. Without continued naval support the ground offensive will almost certainly fail. In addition to continued ortillery, naval aerospace fighters can provide direct close support to ground troops and engage tactical targets in the enemy's rear areas. Marines can conduct assaults against orbital facilities and can even be deployed by drop ships in support of threatened ground forces. If done properly, combined Army/Navy operations can achieve true vertical envelopment.

N-Hour Sequence

The N-hour sequence is a planning tool for military commanders, logistics planners, and political leaders. It is a rough outline of what will happen and when during a particular type of attack. The initial letter may change to determine what type of attack the sequence is for (for example, a ground attack plan can be called a G-hour sequence while a boarding action against an orbital spaceport could be an M-hour sequence). And certain times can be very broad or based entirely upon the success or failure of a different operation. They key to using an N-hour sequence is to remember that it is a tool, not the plan.

This N-hour sequence is, by necessity, abbreviated. It does not include frontier refueling, naval actions on approach to the planet, or orbital combat and boarding actions. It also omits a great many logistical steps that would be included in a ‘real’ sequence, as well as the preparatory steps that occur before the assault fleet enters jumpspace. Again, this is a rough estimation to give an idea of the flow of battle (note: times are given in the form days:hours:minutes or hours:minutes when one day or less. Negative times are before N-hour, positive after):

N –14:00:00:
Assault squadron enters jumpspace.
N –07:00:00:
Assault squadron enters normal space in target system.
N –02:00:00:
Ortillery bombardment begins.
N –16:00:
Decoy deadfall ordnance attacks begin.
N –08:00:
Naval aerospace fighters increase tempo of attacks against tactical surface targets.
N –06:00:
Decision phase: commanders determine if planetary defenses are suppressed enough to allow close orbit insertion of drop ships. If so, drop ships move into close orbit. Bombardment ships direct their fire to both overwhelm defenders and clear a number of possible landing zones.
N –02:00:
Drop troops finish insertion preparation.
N –00:30:
Decision phase: commanders determine if landing zones are prepared and the drop troops are likely to secure an orbit head. If so, drop troops are secured for insertion and troop carriers prepare for drop.
N –00:15:
Naval forces trigger EMP effects.
N –00:05:
Secondary EMP effects are triggered to disable automated responses. Naval forces begin blanket jamming from close orbit.
Simultaneous insertion of drop troops begins, accompanied by numerous decoy insertions with deadfall ordnance accompanied by jammer pods. Naval aerospace fighters deploy for close air support.
N +00:01:
Naval bombardment shifted to cover approaches to landing zones.
N +00:04:
Landing zone prepped by daisy cutters.
N +00:05:
Drop troops begin reaching surface. Drop ships begin move to high orbit.
N +00:07:
Drop troops begin deploying to secure orbit head.
N +00:10:
Drop troops finish landing on surface. Drop troops begin deployment of heavy weapons and support equipment. Aerospace fighters initiate close air support.
N +00:15:
Decision phase: commanders determine if orbit head is secure. If so, landing ships with armor and mechanized forces begin planetary insertion.
N +00:20:
Drop troops complete deployment of heavy weapons and support equipment.
N +00:25:
Drop troops complete initial defensive positions.
N +00:35:
Landing ships begin to reach the planetary surface. Mechanized and armor forces begin to deploy.
N +00:45:
Decision phase: commanders determine if orbit head is ready for deployment of support elements. If so, landing ships begin cycling support units and equipment to the orbit head.
N +01:00:
Combarm begins offensive operations.

It should be obvious that the N-Hour sequence needs to be flexible. Planets with dense atmospheres will require more time for drop troops to reach the surface than planets that have no atmosphere, for example. Deployment of follow on forces may be delayed if there is a threat of significant air defense by the defenders. The number of changes that may need to be made are almost infinite. Recognizing this uncertainty, called ‘the fog of war’, and being able to anticipate and react to change without panic is what separates good commanders from great generals.

Non-Imperial Forces


The Zhodani are very likely to use warbots exclusively in their initial insertion. They have very good warbot technology and prefer to risk machines over their own soldiers. With the capabilities of their elite psionic troops, they are also highly likely to mount a number of commando raids in support of their use of drop troops.


While the Hivers are unlikely to ever engage in planetary assault, if it necessary they will almost certainly use a variety of warbots in every phase of the operation.


After the Rim War the Solomani have a fair amount of experience with planetary assault operations. They will probably use tactics very similar to Imperial forces, but with a greater emphasis on commando operations to offset any advantages in manpower and technology.


Aslan forces are very professional and capable. They will tend to have more landing zones in an attempt to overwhelm defenders with the number of threats rather than with a small number of highly massed forces.


The nature of Vargr command and control means that their planetary assault operations will be less organized. They may actually have waves of insertions coming at different times rather than a mass drop and may have trouble coordinating naval support for ground troops. On the other hand, their desire for personal glory and achievement means that they are more likely to initiate ‘breakout’ actions where they focus on specific target rather than engaging defenders directly. This can force the defenders to commit a significant portion of their forces to protecting targets rather than repelling invaders.

Mercenary Units

While it is extremely unlikely that mercenaries would undertake a full-scale planetary assault, they may occasionally be hired to perform small-scale operations that are very similar in execution, if not scope or breadth of support. And mercenary units in the wrong sub-sector at the wrong time may end up 'assisting' colonial or imperial units during a planetary assault.

Glossary of Terms

Aerospace fighters:
Space fighters capable of atmospheric operations.
Air Defense:
All defensive measures designed to destroy attacking enemy aircraft or missiles within a planet’s envelope of atmosphere, or to nullify or reduce the effectiveness of such attack.
Armor units:
Refers to tank forces.
Artillery unit:
A military unit composed of artillery pieces and their support crews.
Assault ships:
Heavily armed and armored small craft capable of atmospheric operations, usually capable of transporting ground forces. Often used to escort landing ships when there is a high threat of air defense. Sometimes used to land ground troops in enemy-controlled terrain.
Close aerospace support:
The use of aerospace fighters and assault ships to attack enemy ground forces that are close to or in combat with friendly ground forces.
Combat ineffective:
A unit or group of units that is not longer capable of combat operations for any reason.
Combined arms army:
A large ground forces unit composed of infantry, armor, mechanized infantry, artillery, and support units capable of extended combat operations without external support. Often abbreviated Combarm.
Command and control:
The issuance of orders by military commanders. Can also refer to the military commanders themselves.
Deadfall ordnance:
Explosives devices that have no internal propulsion system. They can be launched on specific trajectories, but are usually released into a gravity well and allowed to fall.
Decision phase:
A pre-planned time or place where a choice must be made between two or more military options by commanders.
Heavy infantry:
Infantry with a greater than standard percentage of heavy weapons per unit. Usually refers to battle dress armored infantry.
Heavy units:
In general refers to units with heavier weapons or with the ability to concentrate a great amount of fire in a small area in a short amount of time. Generally used to refer to battle dress infantry and tank units.
Information about an opposing force gathered through observation and analysis. Also refers to the process of gathering intelligence.
The deliberate radiation of electromagnetic energy for the purpose of preventing or reducing an enemy’s effective use of the electromagnetic spectrum, and with the intent of degrading or neutralizing the enemy's combat capability.
Landing ships:
Small craft or spaceships capable of atmospheric operations and surface landings that are configured to carry ground troops and equipment.
Landing zone:
An area designated for drop troop or landing craft insertion.
Light infantry:
Infantry units with a smaller than standard ratio of heavy weapons per unit. Such units also usually have a lighter than standard equipment load.
In its most comprehensive sense, those aspects of military operations which deal with:
  • design and development, acquisition, storage, movement, distribution, maintenance, evacuation, and disposition of materiel;
  • movement, evacuation, and hospitalization of personnel;
  • acquisition or construction, maintenance, operation, and disposition of facilities; and
  • acquisition or furnishing of services.
The process of broadcasting false navigation signals to give inaccurate measurements of locations, speed, distance, etc.
Mechanized infantry:
Infantry units that enter combat zones riding in and fighting from lightly armored vehicles. Such units often have organic armor units.
The broadcast of radiation designed to appear as the broadcast of an opponent, but conveying false or misleading information. Also called Electromagnetic Intrusion.
Orbit head:
A designated area in a hostile or threatened territory which, when seized and held, ensures the continuous landing of troops and materiel from orbit and provides the maneuver space necessary for projected operations. Normally it is the area seized in the assault phase of a planetary assault operation.
Organic support:
Elements assigned to and forming an essential part of a military unit.
Heavy weapons fire from orbit; an abbreviation of orbital artillery.
The rebroadcast or reflection of electromagnetic energy for the purpose of preventing or reducing an enemy's effective use of the electromagnetic spectrum.
The degree of dominance in the aerospace battle of one navy over another which permits the conduct of operations by the former and its related forces at a given time and place without prohibitive interference by the opposing force.
The degree of aerospace superiority wherein the opposing force is incapable of effective interference.