Yes Ken,
you are quite correct. Even though an engineering officer might outrank the IWO, the latter will preceed him as commanding officer until relieved. I dimly recall a reserve medical officer (Abel) assigned to one of the 7cFlak boats (?) succeeded bringing the boat back after CDR, IWO and 2WO were either KIA or severely wounded. Btw, this Abel was the brother of the IWO, who caused the courtmarshal of his CO on political grounds. Doenitz rewarded the brother with the command of his own (U193). He lost his command and the lives of his 59 crew a couple of days after leaving Lorient on his first patrol.
Rgds, RB
Ps: Got your email, will call during the next couple of days. Assume phone # still the same.