Everything you never knew you wanted to know about the Mercury Project
Astronaut window
From RixWiki
The Astronaut window was one of the major changes between the early and later Mercury spacecraft. Early spacecraft had two porthole windows. These were replaced with a single trapezoidal window over the astronauts head.
The only manned Mercury spacecraft which did not have the large window was Alan Shepard's Freedom 7, a.k.a. spacecraft 7.
