Symbols on submarine battle flags

[dmlavan]

Deos anyone know a reference/guide for the symbols on WW2 submarine battle flags? I know the two flags for marus and warships, but on some battleflags the "sun" in the center is empty, i.e. a red border but white inside instead of red. On some others, I've seen what looks like a "T" inside the sun, but cannot find a reference for what these different versions mean.