The Merlin III engine of Spitfire Is had a power rating of 1,030 hp ( 768 kW ) .
Supplies of 100 octane fuel from the United States started reaching Britain in early 1940 .
Although the Merlin III engine of Spitfire Is had a power rating of 1,030 hp ( 768 kW ) , supplies of 100 octane fuel from the United States started reaching Britain in early 1940 .