Errm, not quite.
The defences at Scappa Flow were allowed to be run down during the inter-war period, but when war was declared, things changes pretty quickly.
More block ships were sunk, a new airbase for RAF/FAA fighters and Coastal Command observation aircraft was built, a destroyer squadron and a flotilla of MTBs were based there and the whole area had more AAA than London did until the Battle of Britain started in 1940.