Little America IV. Naval ships and personnel were withdrawn back to the United States in late February 1947, and the expedition was terminated due to the early approach of winter and worsening weather conditions. Byrd discussed the lessons learned from the operation in an interview with Lee van Atta of International News Service held aboard the expedition's command ship, the USS Mount Olympus. The interview appeared in the Wednesday, March 5, 1947, edition of the Chilean newspaper El Mercurio and read in part as follows: Admiral Richard E. Byrd warned today that the United States should adopt measures of protection against the possibility of an invasion of the country by hostile planes coming from the polar regions. The admiral explained that he was not trying to scare anyone, but the cruel reality is that in case of a new war, the United States could be attacked by planes flying over one or both poles. This statement was made as part of a recapitulation of his own polar experience, in an exclusive interview with International News Service. Talking about the recently completed expedition, Byrd said that the most important result of his observations and discoveries is the potential effect that they have in relation to the security of the United States. The fantastic speed with which the world is shrinking – recalled the admiral – is one of the most important lessons learned during his recent Antarctic exploration. I have to warn my compatriots that the time has ended when we were able to take refuge in our isolation and rely on the certainty that the distances, the oceans, and the poles were a guarantee of safety. After the operation ended, a follow-up Operation Windmill returned to the area in order to provide ground-truthing to the aerial photography of HIGHJUMP from 1947 to 1948. Finn Ronne also financed a private operation to the same territory until 1948. As with other U.S. Antarctic expeditions, interested persons were allowed to send letters with enclosed envelopes to the base, where commemorative cachets were added to their enclosures, which were then returned to the senders. These souvenir philatelic covers are readily available at low cost. It is estimated that at least 150,000 such envelopes were produced, though their final number may be considerably higher. Participating units Task Force 68 Rear Admiral Richard H. Cruzen, USN, Commanding Eastern Group (Task Group 68.3) Capt. George J. Dufek,