Adding to Mush's statement (which is a short version/spot-on synopsis

) the Mark 10 was a smaller torpedo than the 14. I
think it was only 18 feet long. Both were 21" diameter. The Mark 10 was designed for the Old S-Class boats which were not able to use Mark 14's (too long for their tubes). Naturally--most of the 10's were than alotted to that class of submarine although there was at least one instance I remember where a fleet-type boat also took a few 10's on board because there weren't enough 14's available.
The 10 was more reliable early war although it too ran about 5-10 feet deeper than it was set to run. Contact Pistol only--they didn't have the Mark VI Magnetic Exploder--so they were immune to that nasty piece of hardware.
Cheers!
Peto