Select the unit and go to the missile deployment section on the top part of the central panel. You can load/unload missiles there.
Ohio class submarines carry 24 Trident missiles.
Aircraft don't always "have" missiles. They are fitted with a mix of missiles or bombs according to each mission. The Tigershark was a fairly small aircraft, close to the ground and had limited hardpoints (where missiles are fitted) It could carry 2 Sidewinders and 2 of either Sparrow or Maverick, but 4 missiles was the limit.
All current missiles are electrically triggered in a sequence to 'spool up' as they release from the aircraft.
As regards torpedoes or missiles, yes, the submarine has weapons that can be launched underwater.
Medium calibre guns (naval artillary), missiles (anti-aircraft, anti-missile, anti-ship), close range guns (automatic - defending against missile/air attack, or manned, for policing duties against smaller craft). Small arms (rifles, pistols). Torpedos, depth charges (anti submarine). Nuclear missiles. Cruise missiles.
Many Anti-Aircraft missiles find their targets based on heat. If an AC130 deploys flares, which are hot, the missiles follow them instead.
procurement
Procument
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You must have torpedoes, stronger missiles, aim for the weakest spot of an aircraft carrier, you must have faster planes with extremely powerful missiles but always keep that in mind about that aircraft carriers are really huge and very strong.
The Commanding Officer, with concurrence from the Executive Officer.
All of these missiles are different sizes, and carry different payloads.