Small quibble on nomenclature: In SLM-1, the Submarine Torpedo Fire Control Manual (
http://www.hnsa.org/doc/attack/index.htm), what you are referring to as the "track angle", (theta sub track on your diagram) is designated the "torpedo track angle". This is distinct from the track angle, which SLM-1 defines as "
The angle at the point of intercept target ships course and the submarine's course measured to port or starboard of the target ship's bow toward the submarine. Symbol: Ta." That is, track angle, as used in the WW2 USN and in many first-person accounts, is relative to the submarine's course, not the torpedo's course. Using the two interchangeably might cause confusion to someone reading first-person accounts or patrol reports.