You can turn your fighter into a heavy bomber that can destroy any structural targets (air bases, railroad stations, and other groups of objects). Enable the "Unlimited ammo" setting in options, then align your plane with your target so that you are flying over its length. For an air base, line up with the runway; for railroads line up with the tracks. Once you are lined up on your bomb run, pick out a target and count down the range until you are a minimum three miles out. The distance you start bombing depends on your altitude, however. As a rule, start dropping at two to three miles. When you start bombing it is recommended that you drop two bombs at once, preferably 1000 pounders. Revive your plane on the proper heading and drop the first bombs. Revive again and then drop. Do this as many times as possible as fast as possible until you are within a few thousand feet of the target or you want to stop. For more fun, enable the "Invincibility" option. Once you drop the last two bombs, roll over and dive, then roll again and pull up a few feet of the ground. You can fly straight through your own stream of bombs and watch them explode at extreme close range.
Enter the museum and test fly the Spitfire, then drop both of the 500 lb. Bombs and expend all ammunition except for approximately nine rounds. Once done, press CTRL + A + E to turn off the engine. The Spitfire will transform into a huge bird that is carrying a bomb.
Note: This procedure requires editing a game file; creating a backup copy of the file before proceeding is recommended. With a text editor, edit the "ww2.ini" file in the game folder. Change the value following the "Unlimited Weapons" entry to "yes".