Tweaking simulations to make results conform with current political or military thinking is a recurring problem. In US Naval exercises in the 1980s, it was informally understood no high-value units such as aircraft carriers were allowed to be sunk, as naval policy at the time concentrated its tactical interest on such units. The outcome of one of the largest ever NATO exercises, "Ocean Venture-81", in which around 300 naval vessels, including two carrier battle groups, were adjudged to have successfully traversed the Atlantic and reached the Norwegian Sea despite the existence of a (real) 380-strong Soviet submarine fleet as well as their (simulated) Red Team opposition, was publicly questioned in "Proceedings", the professional journal of the US Naval Institute. The US Navy managed to get the article classified, and it remains secret to this day, but the article's author and chief analyst of Ocean Venture-81, Lieutenant Commander Dean L. Knuth, has since claimed two Blue aircraft carriers were successfully attacked and sunk by Red forces.