claim: Project Y's mission was to destroy the first atomic bombs.
evidence: A two-stroke , or two-cycle , engine is a type of internal combustion engine which completes a power cycle with two strokes -LRB- up and down movements -RRB- of the piston during only one crankshaft revolution .. internal combustion engine. internal combustion engine. piston. piston. This is in contrast to a `` four-stroke engine '' , which requires four strokes of the piston to complete a power cycle .. piston. piston. four-stroke engine. four-stroke engine. In a two-stroke engine , the end of the combustion stroke and the beginning of the compression stroke happen simultaneously , with the intake and exhaust -LRB- or scavenging -RRB- functions occurring at the same time .. scavenging. Scavenging ( automotive ). Two-stroke engines often have a high power-to-weight ratio , power being available in a narrow range of rotational speeds called the `` power band '' .. power-to-weight ratio. power-to-weight ratio. Compared to four-stroke engines , two-stroke engines have a greatly reduced number of moving parts , and so can be more compact and significantly lighter .