by the Primary Air Reserve in Montreal, Toronto, Edmonton and Winnipeg, with approximately 10 aircraft at each base, as well as by the RSU (Regular (Forces) Support Units) at those bases. It was usually flown with a single pilot (Commissioned Officer) in the left seat and a Technical Air Crewman (NCO) in the right seat. The Kiowa helicopter replaced it in Air Reserve squadrons. Although the Otter found ready acceptance in bush airlines, as in a similar scenario to the DHC-2 Beaver, the United States Army soon became the largest operator of the aircraft (184 delivered as the U-1A Otter). Other military users included Australia, Canada, and India, but the primary role of the aircraft as a rugged bush plane continues to this day. An Otter crossed the South Pole in 1957 (see Commonwealth Trans-Antarctic Expedition). The Otter is also popular in the skydiving community and can be found in many dropzones throughout the world. Otters were used by Qantas from 1958 to 1960 in Papua New Guinea. The Qantas aircraft were then transferred to Trans Australian Airlines (TAA), a major Australian domestic airline, which operated the Otters in Papua New Guinea until 1966 when they were withdrawn from use. TAA was merged with Qantas in 1990. Modifications The most extensively modified Otter was RCAF Otter 3682. After initial service as a standard Search and Rescue aircraft it was used to explore the aerodynamic aspects of STOL. In 1958 it was fitted with flaps so outsized that, with their 45 degree droop, it became known as the Batwing Otter. In addition, its tail-wheel undercarriage was replaced with a high energy- absorption 4-wheel arrangement and a very high vertical tail. The next modification replaced the flaps with fully retractable flaps suitable for cruising flight and high drag was obtained with reverse thrust from a J85 turbojet installed in the fuselage behind the cockpit. The third configuration looked a lot like the future Twin Otter and was the first twin-PT6 fixed-wing installation to fly in May 1963 (A twin PT6-engined helicopter, the Kaman K-1125, had flown in April 1963). The piston engine in the nose was replaced with wing-mounted engines to blow over the flaps. Stolairus Aviation of Kelowna, BC, has developed several modifications for the DHC-3 including a STOL Kit, which modifies the wing with a contoured leading edge and drooped wingtips for increased performance. Stolairus has also developed a "upgross"