Goodness, a quote without a citation so people can't see the context in which this was written. For those not familiar with the document he is describing, it was a memo written by General Schulgen in October of 1947. The purpose of the memo was to determine
the current intelligence requirements in the field of Flying Saucer type aircraft.
The quote is one part of a section that starts with:
Commonly reported features that are very significant and which may aid in the investigation are as follows:
Note the "reported features" and not proven facts. They are just the reported observations, which are subject to error. Additionally, the section quoted has the following after it:
Under certain power conditions, the craft seems to have the ability to cut a clear path through clouds -- width of path estimated to be approximately one-half mile. Only one incident indicated this phenomenon.
Note the bolding.
The section most pertinent in this memo is this:
This strange object, or phenomenon, may be considered, in view of certain observations, as long-range aircraft capable of a high rate of climb, high cruising speed (possibly sub-sonic at all times) and highly maneuverable and capable of being flown in very tight formation. For the purpose of analysis and evaluation of the so-called "flying saucer" phenomenon, the object sighted is being assumed to be a manned aircraft, of Russian origin, and based on the perspective thinking and actual accomplishments of the Germans.
You can read this all yourself here:
http://www.roswellfiles.com/FOIA/Schulgen.htm
As one can see, in 1947, the intelligence community was concerned the observations were of actual craft from the Soviet Union invading US Air space. This was duplicated in another intelligence document under the title of
Air Intelligence study #203 Analysis of flying objects incidents in the US which was written in late 1948 (10 December 1948 even though the document states 1952 and 1949, the original was published then).
http://www.project1947.com/fig/1948air.htm
This is a top secret document and should mention alien spaceships if they actually believed the reports were of these. There is no mention of spaceships in this document. However, there is mention that the reports may be simple misperceptions of existing known craft and phenomenon.
Remember that it was only 6-7 years after Pearl Harbor and 2-3 after the war had ended. The cold war was starting and the USAF was concerned that these reports might mean the soviets were developing something that was superior to their own aircraft. They were not going to dismiss these reports away as misperceptions without some serious analysis of the reports. It was assumed they were somebody's aircraft but it did not mean they were actual craft.