Military Equipment: Do submarines, space shuttles, airplanes and ships have self-destruct systems? If so, what's the purpose of such systems?

I was an engineering officer (not the engineer) on an SSBN and we did not have a self-destruct system. We did have a ship destruct bill, which were instruction for each compartment on how to destroy that portion of the ship before evacuating it.  I remember reading the ship destruct bill in maneuvering. It said something like, "Destroy the reactor as follows..." and then gave step by step instructions on destroying the reactor. I remember thinking at the time, "Yep, that would do it."

To add to 's excellent answer, the F-4 reconn aircraft had a switch in the back seat to blow up the onboard cameras.  I always had the itch to see of it really worked....

In general they don't have them. Self-destruct systems are by definition dangerous and unnecessary for normal operations of most craft.In a ship or submarine it would be simpler just to open something connected to the outside and let nature take its course.  Most crew could easily think of at least a half dozen ways to do this and still have a reasonable attempt at escape.  Aircraft are even easier to destroy.  Point the nose down and gravity fixes things soon enough.  Sure, there are other issues but zeroing and such tends to fix things like "secrets".The things that DO have self destruct systems are rockets and missiles.  These are flying bombs in the first place and if something is headed somewhere you don't want it to be you need a way to terminate that progress in an urgent manner.  The Space Shuttle itself didn't have a destruct system but the solid rocket boosters each did.   A liquid fueled rocket can easily be turned off by shutting down its fuel flow.  A solid fueled rocket, not so much.  It burns until it's depleted or destroyed.  A telling example of this is that the Solid Booster on the Challenger that cause the stack destruction was itself detonated by the Range Safety Officer when it was in danger of turning into a populated area.Destruct systems make good science fiction, but they aren't workable or necessary in real life.  And a significant danger.

While I have no experience with the space shuttle or submarines other than hunting them I can speak about ship. There is no self destruct on ships. Electronic equipment with crypto can be quickly cleared. As for keeping the ship out of enemy hands. Just open up the sea chests which are water intakes for pumps and outlets for dewatering eductors. Add the fact that they have fire pumps it would not take long to sink a ship.

I can only speak for systems I have worked on which are sensitive radars, and we have some specific things to destroy or remove and keep if possible.   Data tapes or hard drives, and the specific points where explosives would be placed to render the device/system unusable and not able for the enemy to learn anything from it.  These instructions are in the manuals for the systems.

Once during a service period, I had the "pleasure" of spending a week-end on guard duty. While on duty at the phone in the guard room, we got really bored but had the right to kill time only by reading service manuals for our equipments.... All included a section on how to destroy or make the gear inoperant, from radios to assault rifles. This is applicable to bigger pieces equipment: it's better to instruct your men on how to destroy them than to implement a self-destruct mechanism, which is prone to malfunctions.

Having served in the Royal Navy as an officer on ships and submarines, we had no self destruct systems installed.  In an SSBN, it was recon'd that you had enough time to say the first two lines of the Lords Prayer should a missile cook off in a tube and rupture the pressure hull.  Thankfully its never occurred!In ships we had lead lined bags with holes in them.  Cryptographic material was supposed to be put in to them so they sank if thrown overboard if capture was a possibility.I understand that there were plans to fit ejector seats to helicopters, and to stop the pilots being shredded, explosive bolts were fitted to the rotor heads.  These did not prove popular and,  I believe, would prove to be an effective self destruct mechanism!

On my US Fast Attack Sub there was no self destruct mechanism, per se', but there was a scuttling process as others have pointed out. We went out with charges set in place such that the few persons trained to finalize arming them could. We weren't as prone to scuttle in port, but we did have a multi-level strategy to "Repel Boarders" we did have to implement once when Greenpeace had publicly announced in advance to do such. And we did have a procedure if "Repel Boarders" was announced for events that had been discovered. That was implemented once when some guys on the Sub Tender we were tied up next to wanted to have some fun with us. The OOD on that Tender had some explaining to do. ;-)

In the US Army we practiced demolition of sensitive weapons, vehicles and equipment with thermite grenades.  These were employed by hand.  The thermite melts the equipment, rather than using an explosive charge which would simply toss the material, and is much more recoverable. So.  No, they do not have self destruct devices built in.