Perhaps I can give you a bit of a hand here. I am a former US Navy sailor (and current US Coast Guardsman) with 8 years shipboard, 3 of which I spent specifically doing internal security (sort of similar to the repel boarders scenario) as well as doing a couple of boardings. In other words, I am intimately familiar with combat on the inside of a ship. I will only speak on that which makes sound tactical sense and avoid getting into anything that might get me into trouble. I’m also in school to be an aerospace engineer, so I know a little something about spacecraft as well.
First, I’ll start by saying that it’s almost impossible to overstate the nightmare factor of a repel boarders scenario. Very high drama, and in my humble opinion, you’d be doing your readers a disservice if you didn’t properly convey the very heavy terror of such an action. BTW, the actual term we use is “opposed boarding,” so I’ll use that from here on. Another terminology note, navy pukes don’t really prepare to do anything. We stand by. The command would be “STAND BY TO REPEL BOARDERS, [PORT/STARBOARD] SIDE!” Gives me chills… Google search images of ship’s passageways and you’ll see why. Very narrow, very Spartan. Not much cover, and what cover there is will not be bulletproof. Although, I will say this: the defenders have a significant advantage in this scenario.
In order to understand the methods of defense that a security team would employ against boarders, it’s most vital to understand the offensive tactics used by a boarding team in an opposed boarding. Sort of a “think about what you would do and do whatever you’d do to stop someone from doing that” kinda thing.
Boardings are undertaken in order to capture a ship before it is destroyed or to avoid destroying it altogether. An opposed boarding is such a dangerous affair that it is generally speaking much more economical to destroy the target. This means you don’t board a ship unless there’s something on board that’s REALLY valuable and can’t be salvaged from the wreck. Your antagonists are going to ENORMOUS lengths to take this ship, and that also deserves mention (IMHO).
But if you insist on boarding a ship, you want to do so as quickly and quietly as possible. A stealthy approach and a hull breach as near as possible to the critical parts of a ship are your best bets.
Now, a little mental exercise: If you want to control a ship, what must you control? The first instinct is to say “the bridge.” Well, that’s a high priority target, but a ship, on the whole, can be run just as effectively from the engine room as the bridge, with a little emergency rigging. So you absolutely have to control the bridge and engine room.
Now, imagine you captured the bridge and engine room, but word got out to the enemy fleet that the ship had been boarded? If it was important enough to warrant an opposed boarding, it is probably important enough to write off the lives of the crew, and thus the defenders’ allies may try to sink the ship to prevent it being taken as a prize (that’s actually what we call a captured ship. The crew that we send to man the vessel after it’s captured is called a prize crew). This party just took a nasty left turn for everybody aboard. So capturing the comms center is also a high priority.
By this time, you can be sure that your presence has been noted by the crew and they have probably pieced together that you launched from a bigger boat than the dinghy attached to the hull, so anyone not involved in repelling boarders will probably attempt to force your retreat by engaging your mothership. So you want to capture gunnery and other combat systems quickly. Another plus to this is that you can then use the ship to fight.
After you capture combat systems, comms, engineering and the bridge, you effectively own the ship. At this point, the defenders have little choice but to fight until they don’t have any bullets left or surrender to the attackers.
Keep in mind that due to the layout of ships, these things rarely happen like in Halo. More often, it will be a VERY small team of special ops types who rely on the element of surprise to achieve their objective.
Knowing that, how might you defend against boarders? Well, the first thing that I would do is order the ship to battle stations, or General Quarters. On my last ship, this involved an alarm and the following was passed over the PA: “General quarters, general quarters. All hands man your battle stations. Set material condition ZEBRA (more on this in a moment) throughout the ship. Below the main deck proceed up and forward starboard side, down and aft port side. Man all damage control repair stations. All stations make manned-and-ready reports to the bridge over [the designated GQ net] or by calling [the bridge’s phone number]. General quarters.”
As a captain responsible for the life and well-being of every man under my command in addition to the life and well-being of the ship and any cargo aboard, my first tactic is to prevent the boarders from breaching the hull. Gunnery should be engaging the boarding craft from the moment they are identified as threats.
Simultaneously, I would have all of the internal doors closed and sealed. All of them. In the US Navy, we call this ‘condition ZEBRA.’ Ships are made watertight (or in this case, airtight) so that if one compartment floods (or decompresses), the damage is isolated to that one room. You can use that against the boarding team. Force them to open the doors. It will slow them down. Once the boarding team loses the element of surprise, they have only speed and violence of action to rely upon. Sealing the doors will slow or even halt their progress.
Once the hull is breached, I would order the doors that are secondary boundaries to the point of entry permanently fused shut. You think about a square room. Say it has three doors (primary boundaries) that lead into the adjoining rooms. The doors out of those rooms are secondary boundaries. Welding these shut will frustrate the effort. In a large-scale boarding, it would necessitate the boarding team bringing cutting tools to the location and beginning the slow work of cutting the door out.
Important note: In a space environment, the use of explosives is probably not very feasible. An explosion kills or injures in one of three ways:
1) Heat: the intense heat can cause severe burns which can incapacitate victims
2) Shrapnel: shards projected outward at high velocity can completely pulverize someone who is very close to the explosion (hence the darkly humorous phrase, “nothing left but pink mist and memories”), and can project small debris for an incredible distance.
3) Pressure: an explosion displaces the air in a spherical area around the device. What is left is a local vacuum, but also a wave of compressed air traveling at the speed of sound throughout the space. This is called an overpressure wave. It can cause death by severe internal hemorrhage and may even vaporize a body, given sufficient energy.
The overpressure wave dissipates harmlessly in an open tactical environment. The wave bounces quite well off of most walls, though. Consider the 20 July plot to kill Adolph Hitler. The bombing in the Wolfsshanze failed because it was too hot in the bunkers so they went to an outbuilding and opened the windows, which allowed the pressure to escape. That, combined with the shielding effect of a sturdy table leg, spared just about everybody in that room including Hitler the brunt of the bomb. Now consider that every habitable space on a spaceship must be pressurized to 14.4 psi (not sure what the metric works out to, sorry) and one has to be very careful about maintaining that pressure. There are not likely to be very many wide open spaces on a spaceship because it takes so much atmosphere to maintain pressure. Breaching explosives would then likely cause severe injury to both the boarding party and the defenders. Perhaps some class-delta burner or acid to eat through the bulkhead is more appropriate than breaching explosives.
Doors are a defender’s best friend. It forces the hostiles to go single file through a very narrow space. In fact, on modern warships, an average sized person can barely get through a door without bending, twisting, jumping, or otherwise contorting themselves. This means you can maul anybody passing through with hostile intent. Shotguns are a natural choice to defend this. Many passageways on a ship intersect with others, forming 4-way and “T” intersections. These corners are the best cover that you’ll typically find in any ship. If your defenders are wearing proper hearing protection, you can get three men behind each corner. One in the standing position, one in the kneeling position, and one in the prone position. This will not be comfortable for long, but it will provide a fairly heavy volume of fire through the door.
Hopefully that will be enough to get you started. Let me know if you need anything else!
