that impacted on aerodynamic efficiency and, as the numbers of large airports increased, the land plane steadily replaced the flying boat. By the late 1930s, civil passenger transport was largely by land planes and the flying boat was restricted to the great long distance flights from Europe to Africa and Australia. There was, and continues to be some attraction in operating flying boats, or amphibians, in the Pacific where the host of tiny islands makes it difficult to construct landing strips capable of taking aircraft with the range to fly between islands. The flying boat and amphibian also continues to offer advantage in specialist operations, such as fire fighting, where the aircraft can land on a lake or the sea and refill its fire-fighting tanks as it taxis to take off again. In the late 1930s, the flying boat was also seen as an essential maritime patrol and naval bombing aircraft. A British Air Ministry requirement in 1933 called for a general-purpose four-engine flying boat, capable of operating from the remote outposts of Empire. Shorts developed the outstanding Sunderland flying boat to meet this requirement, using research and design started to build the Short Empire flying boat for commercial passenger transport. The Sunderland was a large deep-bodied monoplane with four powerful radial engines and three power-operated gun turrets. Although the deep body presented a large surface area, drag was contained by avoiding the bracing wires and struts that were an unavoidable feature of bi-plane flying boats of the time and