In Torpedo Alley the player commands a submarine in hostile waters, with one objective: sink as many enemy ships as possible. The sub is armed with a limited cache of torpedoes, and as enemy ships zig-zag across the periscope view, each launch must be timed accurately to intercept its target. If a ship makes it halfway across the screen without being sunk, it spots the player's sub and starts shooting; any damage will destroy some of the remaining torpedoes. The only way to evade enemy fire is to dive deeper. When the sub is fully underwater, the 1st-person periscope screen is replaced with a side view, where the player maneuvers to avoid depth charges placed by the enemy: a single charge means certain death if it hits. When the sub is destroyed (or runs out of torpedoes) the game is over.