...The Germans were one of the few nations to specify a paint doating for their torpedoes. Many were in bare metal. German torpedoes showed a lot of bare metal, too. As little as the warhead casing, and the tail cone & fixed fins were painted.
The most extreme "bare metal" use was the US. Until late 1942, all US torpedoes were made in the US Navy Torpedo Shop. Who were not fast, nor innovative, nor musch interested in changing their ways (hence the Great Torpedo Controversy in the Pacific). Lots of bronze, phosphor-bronze, and monel in US torpedoes.
You can lightly oil stowed torpedoes, but only enough for corrosion prevention. This, because you have to be able to bend tackle on to put them in the hoist racks (put a tonne or two of torpedo over men's heads and you do not want the chains to slip).