The Sikorsky S-43 had to be boarded from a top hatchway because it was an amphibious seaplane

The Sikorsky S-43 had to be boarded from a top hatchway because it was an amphibious seaplane,

meaning that it had wheels and could land on a concrete runway, or be a flying boat and land in a bay. Only Sikorsky's aircraft could do this. The Martin M-130 and Boeing B-314 seaplanes could only land on water. The U.S. Navy also had a number of these seaplanes, which were based at Pearl Harbor, Hawaii and used mostly as small fleet transports and for target towing.

The S-43

in Hawaii

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The Sikorsky S-43 "Baby Clipper". The Sikorsky S-43 had to be boarded from a top hatchway because it was an amphibious seaplane, meaning that it had wheels and could land on a concrete runway, or be a flying boat and land in a bay. Only Sikorsky's aircraft could do this. The Martin M-130 and Boeing B-314 seaplanes could only land on water. The U.S. Navy also had a number of these seaplanes, which were based at Pearl Harbor, Hawaii and used mostly as small fleet transports and for target towing.