 However , landing paratroopers , and especially gliders , without the cover of darkness left them exceedingly vulnerable to anti @-@ aircraft fire . The official history of the British Airborne Divisions highlights the cost of this trade @-@ off , stating that of the 416 gliders that landed , only 88 remained undamaged by enemy fire , and that between 20 – 30 percent of the glider pilots were casualties . Another historian argues that the gliders landing in daylight was a calamity , with the 194th Glider Infantry Regiment having two @-@ thirds of their gliders hit by ground fire and suffering heavy casualties as they landed . The casualty rates were worsened by the slow rates of release and descent of the gliders themselves , and the fact that each aircraft towed two gliders , slowing them even further ; as the time to release a glider unit was 3 – 4 times longer than a parachute unit , the gliders were vulnerable to flak . 
