Do First Sea Lords automatically sit in Parliament?

Do First Sea Lords automatically have a seat in the House of Lords?

No. They do not automatically sit there now, although knighthoods are common; earlier officers such as Beresford could combine naval service with parliamentary office.

Modern convention differs from the looser political boundaries visible in Beresford's career. Beresford served as an MP while still a naval officer, something that was not unusual in that period. A First Sea Lord today does not automatically receive a seat in the House of Lords. Senior officers often receive knighthoods, but this is customary rather than guaranteed.