Captain Crane orders four torpedoes readied for launch. He calls out their launch one at a time. After Crane calls out the first torpedo launch, we see four torpedoes launched from the Seaview at the same time. Crane continues to call out the rest of the torpedo launches, even though all four have been launched together.
Visible wires on the torpedoes fired by the Seaview.
When the Seaview's torpedo strikes the enemy sub, the enemy sub explodes. But the torpedo itself never explodes.