(Tribune News Service) — From the fantail of USS Gerald R. Ford, as F/A-18s roar past a few yards overhead, Chief Warrant Officer Todd Williamson was testing the carrier’s last line of defense. Making sure the Close-in Weapons System Mount 23 — a combination multiple-barrel cannon, capable of firing 4,500 rounds a minute, tied to radar and computers — can do its job of knocking down missiles or aircraft is just one part of one of the last big tasks in the carrier’s year-and-half long post-delivery test and trial period. Williamson and his team are in the midst of combat systems qualifications — making sure Ford’s guns, radar, communications and command and control systems can do what the