For the completists among us all, here are some of the also-rans, most are crap, but the odd one or two are okay:
The Bedford Incident
Above us the Waves
Agent Red
American Heroes: submarine
Assault on a Queen
Below
Counter Measures
Forty Ninth Parallel
Full Fathom Five
Gray Lady Down
Hell and High Water
Hostile Waters
In Enemy Hands
Landfall
Lorelei: The Witch of the Pacific
Murphy's War
Mystery Submarine
Operation Petticoat
Sub Down
Submarine
Submarine 707R
Submarine Attack
Submarine Raider
Submarine X-1
Submerged
The Abyss
The Atomic Submarine
The Fifth Missile
The Flying Missile
The Last U-Boat
The Phantom Submarine
The Rescue
The Rift
Silent Service
The Valiant
Trapped in a submarine
Two-man submarine
U-Boat Prisoner
Chock