What do you call the guys who can't make it in the Marines? The Army. The Marines get all the love in Traveller. But how do the two services compare?
Both services seem similar on the surface. They shoot at people and get shot at. They are very different in their missions and mentality. The Marines are designated to board vessels and defend their own vessels and naval installations. In time of war they are used to disrupt communications and grab a beachhead for main invasion forces. They are basically aggressor forces and see a lot of combat. They have a worse survival roll than any service except the Scouts
The Army has worse PR. Their main job is to defend their planet against invasion. If they do it right no sane enemy will attack and so no one knows what a great job they've done. Their survival rolls are no worse than any other service and lower than the Marines. So much of their career is fairly peaceful.
More tellingly the Army is a full independent service. They not only maintain and guard their bases they build them on many worlds. In the case of the Marines they often if not always operate out of Navy bases and the Navy deals with much of their logistics and supply.
The Personal Development table for Army and Marines are identical with one difference: the Army replaces blade combat with and Education boost. In fact the Army survival roll is modified, not by Endurance or any physical stat but by Education which reflects the importance of technology in their operations.
In the Service Skills table the Army is again similar to the Marines, but the Marines have blade combat and vacc while the Army has air/raft and forward observer. Again this reflects the Army's role in defending their planet. While the Marines are piling into drop capsules clad in battledress the Army is operating GCarriers and speeders, engaging enemy fighters and fighters launching artillery strikes on enemy vessels and landing forces.
The Marines love their blade weapons. The cutlass is not only handing for hacking stuff, it exemplifies their warrior code. They will do or die. They fight to win.
The Army is the last line of defense. They will make their world too costly to take and hold. After organized resistance ends many worlds have contingency plans for their surviving forces to go underground and mount insurgency campaigns. The Army fights to live another day. They are quite happy letting the other guys die for their cause.
The Army is all about giving their people the skills they need to survive. While the Marines service skills are cutlass and revolver the Army offers their soldiers auto rifle and SMG. Both weapons afford a decent chance of penetrating battledress, are much more affordable than laser weapons for the mass of soldiers that must be equipped, and are more portable for troops not wearing powered armor. Yes the Army has their traditions too but they don't let them dictate their tactics or weapons.
The Army in less forgiving moments refers to its Marine cousins as fools who bail out of perfectly good spacecraft. The Marines refers to their planet bound cousins as ground pounders. In practice both perform the same duties. Marines will defend their ships and bases and Army troops will embark on assaults and invasions