Marshall recognized the need for underwater simulations of extra-vehicular activities (EVAs) and developed three successively larger tanks for the purpose.

Special systems were integrated into the tank for underwater audio and video, pressure-suit environmental control and emergency rescue and treatment.

Visitors and other issues disturbed those efforts, and they moved the operation to McDonogh School where Scott Carpenter was the first astronaut to participate suited.

[9][10][11][12] Meanwhile, MSFC was looking ahead to the Apollo Applications Program which would involve EVAs to convert a mostly-empty S-IVB rocket stage into a space station, and the people designing the hardware needed a thorough understanding of the challenges of weightlessness.

November 1965 tests included removal of the ST-124 and a J-2 engine propellant utilization valve - early steps in a nascent Skylab mission, then called S-IVB orbital workshop.

[3]: 1965-11 p. 18 [13]: p. 189 After the utility of the technique had been demonstrated, in January 1966, workers repurposed a larger explosive forming tank for neutral buoyancy testing.

The MSFC Manufacturing Engineering (ME) lab developed a constant pressure valve which "made it possible to maintain neutral buoyancy at any depth."

Bean was "quite enthusiastic and outspoken about neutral buoyancy as one of the mandatory methods of simulation for all the S-IVB Workshop experiments," according to Manufacturing Engineering director W. R. Kuers.

Stocks, the controller for that exercise, reported Bean's dive began with a leaky glove followed by his Mark IV suit tearing under the arm and requiring diver-assisted evacuation.

Though Alan Bean had visited and consulted on the project, the intent of the simulator was not astronaut training but to verify that "the MSFC developed hardware is safe, simple to handle, accessible, and trouble-free," wrote F. Belew in his March 13 report to von Braun.

Due in large part to Bean's enthusiasm for the project, the Manned Spacecraft Center coordinated with MSFC to provide two astronauts on an as-needed basis, medical support, crew quarters, and safety consultations for simulations.

55, 190 Ed Buckbee wrote that the funding irregularities "prompted a GAO (Government Accountability Office) audit and reprimand, but contributed to the Marshall lore of creativity and pragmatism in getting the job done."[13]: p.

Workers had to develop new techniques to assemble parts underwater because of the low clearance between the top of the tank and the enclosing building's roof.

Paul Weitz and Joseph Kerwin donned Apollo A5L suits (predecessor to the Apollo/Skylab A7L) and practiced film retrieval by both parallel rails and the trolley system while Edward Gibson observed in scuba gear on March 4, 1969.

For example, on August 6 and 7, 1969, astronauts Owen Garriott, Walter Cunningham, and Rusty Schweickart evaluated the Apollo Telescope Mount EVA film retrieval system.

[3]: 1969-08 p. 27 The simulator's hyperbaric chamber saw its first use for its intended purpose the night of September 24–25, 1969, when a TVA worker suffering decompression sickness near Knoxville was airlifted to MSFC for treatment arriving about midnight.

[15] The crew of Space Shuttle mission STS-41-C spent months training for the capture, repair, and release of the Solar Max satellite including practicing using the Manned Maneuvering Unit.