Project Blue Book Case #6506. On September 13, 1959, witnesses at Gills Rock, Wisconsin — the northernmost community on the Door Peninsula, jutting into Lake Michigan — observed a bright object moving over the waters of the lake. The peninsula's remote, narrow tip provided an unobstructed view across the open lake in nearly every direction.
Gills Rock sits at the end of a 75-mile peninsula separating Green Bay from Lake Michigan proper. The community's isolation and the dark skies over the surrounding waters created exceptional conditions for aerial observation. The nearest significant air traffic corridors were over the lake itself, carrying flights between Chicago and the Upper Peninsula, and witnesses were familiar with the appearance of these aircraft.
The object's brightness and behavior set it apart from conventional traffic. It moved in a manner inconsistent with the straight-line commercial routes or the Coast Guard flights that occasionally patrolled the waters around the Door Peninsula's treacherous shipping passages.
The late 1950s was a relatively quiet period for Blue Book, between the dramatic 1957 wave and the resurgence of activity in the mid-1960s. Cases from this inter-wave period, while less numerous, often received more careful investigation due to the lighter caseload. The Gills Rock sighting was documented and investigated without the time pressure that characterized wave periods.
No aircraft or atmospheric phenomenon could account for the observation. The case was classified "Unknown."