In 1915 the Ordnance Survey tidal observatory was established in the harbour and for the next six years measurements of tidal height were taken every 15 minutes.6
In 1937 the fishing vessel Rosebud sailed to London to deliver a petition to the Minister of Health on behalf of those villagers whose homes were threatened under the government’s slum clearance scheme.
During World War II Newlyn was a base for the Air Sea Rescue craft covering the Western Approaches. The harbour was bombed during the war, hitting the collier ‘Greenhithe’, which was beached in the harbour at the time and supplied coal to the east coast drifters, which traveled to Newlyn during the mackerel fishing season between the wars. Reporting the event on the Germany Calling propaganda broadcast Lord Haw-Haw announced that the Luftwaffe had sunk a British cruiser in Newlyn harbour.