Complex sentence: During the Battle of the Marianas, the D4Ys were engaged by U.S. Navy fighters and shot down in large numbers.as faster than the Grumman F4F Wildcat, but not the new Grumman F6F Hellcat.
Split into simpler sentences: During the Battle of the Marianas, the D4Ys were engaged by U.S. Navy fighters and shot down in large numbers. The D4Y was faster than the Grumman F4F Wildcat, but not the new Grumman F6F Hellcat.