Deferred maintenance made wartime defence more expensive

The 1941 defence map looks formidable, with booms, blockships, indicator loops, anti-submarine nets, and heavy anti-aircraft guns. Those systems were not all in place when U-47 entered Scapa Flow in 1939. Naval treaties did not bar Britain from defending its home ports; the weakness came from spending and maintenance choices. Spreading repairs and upgrades across the interwar years could have cost less than emergency construction amid wartime inflation. Deferred maintenance created a readiness failure and a larger eventual bill.