Southwest Airlines flight 149, a Boeing 737-300, N368SW, experienced a failure of the nose landing gear during pushback from the gate at the Baltimore/Washington-Thurgood Marshall International Airport, Maryland, USA. The aircraft was substantially damaged and there were no injuries to the 6 crewmembers or 129 passengers but the airplane was substantially damaged. According to the flight crew, as the pushback tug was maneuvering the aircraft off the gate, the flight crew felt the front of the airplane bounce up and down, and then came to rest on the nose. The passengers were deplaned via air stairs. The nose gear collapsed in a forward direction, resulting in substantial damage to the gear structure, the nose gear well, and crushing the forward bulkhead. An airport surveillance camera video was obtained, which showed the tug pushing the aircraft at approximately 6 knots. The tug specifications indicate that speed could be achieved only in second gear or higher. The airline general operating manual specifies that pushback must be conducted in low or first gear, and at a walking speed. As a result of the damage sustained, retirement of the aircraft was moved forward. PROBABLE CAUSE: “The tug operators excessive speed during pushback.”