Occupying Iceland (1941)

Did you know that in July 1941 (i.e., months before Pearl Harbor) that U.S. forces occupied Iceland to protect north Atlantic shipping routes to Britain?

Now this was with the consent of Iceland. Not an invasion. But my question is, was this "deployment" made without congressional approval? And if so, what was the legal justification/basis for the president's order to do this? I'm sure this was commander-in-chief power, but this was 1940, not 1967 (or 2002). Before we usually think of presidents using this power so, well, expansively.

BTW, this comes up because I'm reading about the 1940 election and the main contenders for the GOP nomination--Wendell Willkie, Robert Alphonso Taft, Thomas Dewey, and so on, and I was just now reading about how the isolationist Taft reacted to the occupation of Iceland.

Taft (from James T. Patterson, Mr. Republican (1972, 245): "The people seem to regard Iceland as an island off the coast of Maine. What concerns me is that if the president can do that in Iceland, he can certainly do it with Ireland, and England itself."

Taft has a point. The commander-in-chief power is a dangerously expansive one, and opposition members of Congress are right to question its expansive uses by presidents.

Update: The U.S. Marine Corps put out a WWII commemorative series in the 1990s, and it includes a "pamphlet history" called Outpost in the North Atlantic: Marines in Defense of Iceland, by Col. James A. Donovan, U.S.M.C. (Ret.). There are some interesting details about the mission to Iceland, including that the U.S. flag was not flown over U.S. barracks in case German spy planes flew over, which they occasionally did. This was a joint U.S.-British-Canadian operation, and the U.S. didn't want it's participation to be that apparent. Iceland was within reach of German paratroopers, staging from bases in Nazi-occupied Norway (occupied early 1940). The Germans never did invade Iceland, though.