Initial engagements with the Luftwaffe had showed the Hurricane to be a tight-turning and steady platform, but the Watts two-bladed propeller was clearly unsuitable. At least one pilot complained of how a Heinkel 111 was able to pull away from him in a chase, yet by this time the Heinkel was obsolete. At the start of the war, the engine ran on standard 87 octane aviation spirit. From early 1940, increasing quantities of 100 octane fuel imported from the U.S. became available. In February 1940, Hurricanes with the Merlin II and III engines began to receive modifications to allow for an additional of supercharger boost for five minutes (although there are accounts of its use for 30 minutes continuously).