Torpedoed ships do not necessarily have massive casualties - when HMS Ark Royal was torpedoed and sunk in November 1941, only one member of her ~1500 strong crew was lost. The primary determinant of how many casualties there would be was how quickly the ship sank. If the ship sank quickly, then few men would make it off. If, as with SMS Pommern at Jutland, the torpedo detonated the magazine, this was almost certain. However, if the ship flooded slowly, the majority of the crew could evacuate. It took just under 12 hours for Ark Royal to sink, giving the crew every chance to make it off. In comparison, HMS Courageous sank in 20 minutes, with 519 casualties from a crew of 850. Similarly, when HMS Barham was torpedoed, it took just four minutes for her to capsize before her magazine exploded. This sinking caused over 800 casualties from a crew of over a thousand. Another factor, especially on smaller ships, was where the torpedo impacted. Should the torpedo hit a crowded mess or canteen, then heavy casualties would ensue. For an example, on the 11th June 1917, the Japanese destroyer Sakaki was torpedoed by the Austrian U-27 in the Mediterranean. The torpedo hit her bow, where her main mess was found. At the time of the torpedo hit, it was very crowded, and while the ship survived, there were 68 casualties aboard.

Once crews made it into the water, survival depended on a number of factors. The typical warship of WW1 and WW2 didn't carry enough boats for the entire crew. Additionally, those that were carried were difficult to launch from a sinking ship. Should other ships be present, then they could contribute their own boats, or come alongside to take the crew off - as Legion did with Ark Royal. From 1915, Royal Navy vessels began to carry primitive life rafts, called Carley floats. These rafts would float off a sinking ship, and could be reached by men in the water. While they kept men afloat, they offered little protection from the elements, being open rafts that required half the men it supported to stay in the water. Life vests and belts had similar flaws (life belts, like those issued to the RN from 1939, also failed to support the head, meaning that sleep or unconsciousness could be deadly). Especially in colder waters, the prime killer was not drowning, but hypothermia. Should the crew not be rescued promptly, then many would die, even if they could swim or had access to a flotation device. When the British destroyer Wild Swan was sunk in 1942, the full crew made it off before she sank. However, rescue took 13 hours, in which time 31 men had died of hypothermia, and another 3 drowned through exhaustion.

Modern ships are generally far more survivable. Increased subdivision and better damage control techniques and provision mean that ships take longer to sink. This means that crews have longer to make it off the ship. Better emergency lighting and better training in escape routes mean that it's easier for crews to escape from below decks. Ships have more life rafts, and easier access to life vests and survival suits. The life rafts available keep survivors warm and dry out of the water. Helicopters make SAR much quicker. All of these improvements can be seen in the Falklands War. HMS Coventry, struck by 3 Argentinian bombs, capsized in 20 minutes. Of her crew of just under 300 men, only 19 died. Compare this to the loss of Courageous in WW2, which sunk in a similar length of time. When ARA General Belgrano was torpedoed by HMS Conqueror, the majority of the 323 losses aboard were in a number of messes around one of the torpedo impact sites. The remainder of the crew abandoned ship safely, and endured up to three days in their life rafts with little incident.