Speaking of submarines, there are the Japanese miniature subs of WW2. 2 torpedo tubes allowed a good punch. One of these torpedoes hit USS West Virginia at Pearl, another hit and severely damaged the British battleship HMS Ramillies in May 1942.
Some 80 Japanese miniature subs in drydock at the end of WW2.
The HA-19 after the attack on Pearl Harbor
We actually caught one on an uncharted Pacific Island, but the SWO - who had recently failed height/weight standards - was unable to fit inside for the 3 hour tour back to Hawaii.