The XBT-1 specification for vertical carrier dive bombing

The Navy required a carrier dive bomber that could descend vertically with zero lift while speed brakes held it below 250 knots. It had to withstand a nine-g pullout with a thousand-pound bomb and carry a mechanism that displaced the weapon clear of the propeller arc. The attack began at about 20,000 feet, with the pilot extending the brakes and progressively steepening the dive while tracking the target. Bomb release at 3,000 feet was followed immediately by a pullout that imposed heavy loads on the airframe. Target movement and wind added to the pilot's task. For Heinemann, designing brakes large enough to control the descent was a central uncertainty at the outset.