The Ship Model Forum

Well, this idea is nothing new when it comes to submarine warfare; the Germans used "merchant submarines" already during WW1 and had the "Milchkuh" tanker subs in WW2. There were also a number of different supply subs in the IJN. Check out the following:

- D1 type (I-361); transport; 2215t subm., 82t cargo
- D2 type (I-372); transport; 2240t subm., 110t cargo + 150t gasoline
- Sen-Ho type (I-351); tanker; 4290t subm., 27t cargo + 365t gasoline
- Sen-yu-sho type (HA-101); transport; 493t subm., 60t cargo
- Maru-Yu type (Yu-1); transport; 370t subm., 40t cargo

The subs big advantage is definitely their invisibility, but their relatively small capacity limits the use. The IJN planned to used them to supply small island garrisons, the I-351 class was intended as seaplane tenders. Modern and bigger subs (e.g. Russian) could carry a lot more cargo and might really be useful in special occasions. Not sure if anything comparable to the WW2 subs is out there today...

If a war ever happened, replenishment ships would be near the top of the list for enemies to sink. Destroy the adversaries capability to resupply and your enemy loses the capability to continue the fight due to lack of gas, water, ammo, food, etc.
Replenishment ships are slow, limited defensive armament or none at all, and are just plain sitting ducks.
What if existing or new submarines could be built as replenishment vessels instead with the capability to carry oil and other assorted cargo? They'd be harder to find and destroy since they're underwater. Only time they'd have to surface is for replenishing another ship. What do you think?