A submarine tender is a type of ship that supplies and supports submarines.
Submarines are relatively small compared to most oceangoing vessels, and generally do not have the ability to carry large amounts of food, fuel, torpedoes, and other supplies, nor to carry a full array of maintenance equipment and personnel. The tender carries all these, and periodically meets up with a submarine at sea to replenish it.
With the increased size and automation of modern submarines, plus their reliance on nuclear power, tenders are no longer as necessary as they once were.
Submarines are relatively small compared to most oceangoing vessels, and generally do not have the ability to carry large amounts of food, fuel, torpedoes, and other supplies, nor to carry a full array of maintenance equipment and personnel.
With the increased size and automation of modern submarines, plus their reliance on nuclear power, tenders are no longer as necessary as they once were.
Submarines at periscope depth in clear water during the daytime are more easily detectable by aircraft that are directly overhead.
Submarines did not have a major impact on the outcome of the war, but did portend their coming importance to naval warfare and increased interest in their use in naval warfare.
Submarines are popular subjects for films due to the danger, drama and claustrophobia of being on a submarine, and the suspense of the cat-and-mouse game of submarine or anti-submarine warfare.