Offshore wind farms will double as radar defence systems in a pioneering deal involving the Ministry of Defence, which previously opposed the erection of almost 1,000 wind turbines off the UK's eastern seaboard because of fears over their ability to scramble defensive radar. Wind energy projects across Britain have been held up for years because of planning disagreements, some concerned with interference from turbines that can baffle air-traffic control and defence systems, creating blind spots or 'blackout zones' in coverage. The wind-driven turbine blades can rotate at up to 200mph, mimicking on-screen the appearance of slow-moving aircraft and showing up as a blur of images. Simply discounting the clutter is dangerous because the images obscure patches from which planes could suddenly emerge; there are fears that hijacked airliners or bombers could evade detection. But now the wind farm industry will spend at least �16m on advanced radar defence systems to be integrated into new offshore wind farms, clearing the way for a significant boost in the UK's supply of renewable energy. The agreement involves a consortium of windpower firms purchasing US-manufactured Lockheed Martin radar equipment so that Britain's eastern airspace approaches can be protected after turbines are erected around the Wash. In return, the MoD has lifted planning objections to five new offshore wind farms that will include almost a 1,000 wind turbines. The deal is expected to trigger a fresh wave of applications to install wind farms. The RAF and the renewable energy industry have been negotiating for years over the problem. A number of technical fixes are being explored, including applying radar-absorbing material to turbine blades to render them invisible to radar.