Complex sentence: Trials of the "America" began 23 June 1914 with Porte also as Chief Test Pilot; testing soon revealed serious shortcomings in the design, it was under powered so the engines were replaced with more powerful tractor engines.
Split into simpler sentences: Trials of the "America" began 23 June 1914, with Porte also as Chief Test Pilot. Testing soon revealed serious shortcomings in the design; it was under powered and so the engines were replaced with more powerful tractor engines.