game balance. Crawford estimated in 1987 that he had worked a total of 800 hours on Eastern Front, and believed that the game had influenced the industry to simplify user interfaces and prove that there was a market for an "intelligent", non-action game. Crawford approached Atari about selling the game, but the company believed that wargames for Atari computers would not be popular. Release Atari Program Exchange (APX), a separate Atari unit that distributed third-party applications, published it on disk and tape. Renamed Eastern Front shortly before release, APX began selling the game in August 1981. It was immediately successful, selling over 60,000 copies with in royalties to Crawford. By June 1982 it was APX's best seller; APX's manager later said that Eastern Front and De Re Atari "paid the bills, i.e. were our biggest sellers". Crawford stated in 1987 that the game had been the most lucrative for him "by at least a factor of four", and in 1992 that it had sold "fabulously well — far better than anybody (myself included) expected", with most purchasers not traditional wargamers. The game was so successful that Atari asked Crawford to convert it to ROM cartridge as an official Atari product. To improve the gameplay he revamped the AI code, and eliminated the ability to "fast forward" the game and avoid combat. Five difficulty levels are added, the "learner" mode with a single German unit in order to teach the user how to use the controls, and each level above that adding more units up to "advanced", which is identical to the original game. In the highest level, "expert", air force corps () are added, and the units can be placed in one of several modes; normal, assault, or defend and move. In "expert" the user can also choose to start in either 1941 with the standard opening, or 1942, with fully developed lines deep within Russia. The new version also adds the ability to save and restore games, colored cities to indicate ownership, and added city names (previously visible only in the manual) to the in-game map. Reception Eastern Front received critical praise from contemporary magazines. Computer Gaming World in 1981 called it "to this date, the most impressive computer wargame on the market". The review praised the graphics and the artificial intelligence, noted its pondering, and suggested that the game was a killer app for Atari computers. Six years