It’s often better to have three 25% chances of sinking the other guy than one 50% chance.
Three 25% of sinking is the same as three 75% chance of not sinking. Which is (3/4) * (3/4) * (3/4) chance of not sinking, which is approximately a 42% chance of not sinking, which is a 58% chance of sinking. 58% > 50%, the math checks out.