Board Thread:Critique and Advice/@comment-5940646-20161026204618/@comment-25252114-20161027192102

Space Combat? That is a very vauge term, as it covers anything from boarding actions, to full on naval engagments. But since you mentioned boarding action, that is what I will cover.

So basically, the first and most important issue when boarding an enemy ship is how you breach it. Now in 40k you have to remember that starships are several kilometers in lenght and have hulls that can be several dozens of meters in thickness in some areas. So it is unlikely that any sort of man-portable explosive would be able to do sufficient damage to break through.

Assuming that you do manage to breach a ship, you also need to remember that they are crewed by thousands if not millions of individuals, depending on the class of ship, and the faction that controls it. Now while Space Marines are very adept in the close quarters combat found in ships, especially those clad in Terminator Armor.

But if attacking a Chaos or Ork Controlled ship, the defenders will likely have something similar in their arsenal, not to mention they will have the numbers on their side. And even should boarding be successful, getting to the main systems of the ship. (Engines, Life Support, Ect.) the enemies will likely have dug in.

The same reason why Space Marines aren't typically used in drawn out siege warfare, while they are well armored and well equipped, their numbers are their weakness. With only 1000 Marines at most, they will simply be grinded down over time by dug in enemy forces.

This is also why even with an Impressive array of ships, including some of the most powerful ships in the Imperium, they typically do not engage in open naval warfare by themselves, without Imperial Naval Support. While the loss of any ship in the Imperium is bad, the ship can easily be replaced, and the crew as well. But if a group of ships controlled by Space Marines were destroyed, that is not so easily replaced.