Newly released photographs show how a team of World War II experts disrupted Nazi plans to bombard Britain - with the help of 3D glasses like those in modern cinemas. Their secret weapon was a stereoscope - a simple Victorian invention which brought the enemy landscape into 3D. Working on the same principles as modern-day 3D glasses, it allowed the PIs to measure height, especially of unidentified new structures - such as rockets and their launch sites.
From UK, you may watch the documentary on the BBC Player until Tuesday 24 May 2011. The last broadcast is on Tuesday, 23:20 on BBC Two.