After Gemini IX-A, Major General Ben Funk had begun to worry  about the chances of ever flying the Air Force's AML in the Gemini program. Gilruth assured him that it would be given every consideration because "extravehicular activity [is] a primary objective of Gemini XII." When Collins had so little trouble on the Gemini X EVA, hopes that the unit would get its chance to fly had revived. But when Gordon suffered exhaustion and overheating, the EVA question was again as wide open as Cernan had left it. Was there some mystery here that the Gemini engineers had not been able to unravel? Several years later, Elms said that no history of Gemini would be complete without a discussion of what he called the EVA Review Board.50 In truth, that may well be a fitting name for the Gemini Mission Review Board before the program's final flight.
The board's first premission meeting for Gemini XII was held in Houston, where the members were being briefed on the maneuvering unit at the exact moment when Gordon was struggling with the umbilical exercise on Gemini XI. Although McDonnell had made all the spacecraft changes that Collins had suggested, they did not seem to be making Gordon's tasks much easier. But talking and guessing were futile, and the board soon returned to the subject on the agenda - the AMU, which, it conceded, "appeared to be a well qualified piece of space hardware . . . although complex of operation."51
At their next meeting, the four men* virtually became the EVA review board that Elms recalled. They "agreed that the EVA experience from previous missions was the only factor having serious potential impact on the Gemini XII Mission." Their first recommendation was to strike the AMU from Gemini XII52 because the pilot's chance of getting into it and using it successfully seemed small, because the unit's potential value could not offset the risks involved in its use, and because the 120 minutes of EVA planned for the final mission should be devoted to a series of simple tasks that could be measured accurately in terms of workload. Mueller agreed with the board and, on 30 September, told the Air Force why the AMU was being deleted from Gemini XII:
It is noteworthy that past EVA has revealed problems that appear less yielding to straightforward engineering solutions than other problems encountered in the Gemini Program. The EVA tasks planned for Gemini were designed to become increasingly complex and demanding on succeeding missions. And, although the experience gained on a particular mission has been carefully applied to later missions, the result has proven less than completely successful. In fact, it becomes increasingly apparent that the techniques and  procedures devised for EVA have evolved from analyses, theories, and experimental concepts that in certain critical instances, and for reasons currently beyond our grasp, are not entirely accurate. Consequently, I feel that we must devote the last EVA period in the Gemini Program to a basic investigation of EVA fundamentals . . . through repetitive performance of basic, easily-monitored and calibrated tasks.53While the board was being briefed on the AMU at its first meeting, Aldrin was practicing with it under water in a swimming pool at McDonogh, Maryland. Later a flight-ready unit was installed in Spacecraft 12's adapter at Cape Kennedy. On 23 September - the day Elms sent the review board's recommendations to Mueller - it was pulled out. Aldrin, who had once worked in the Air Force experiments office in Houston, was disappointed at the loss of the AMU. He was also concerned about what was to take its place in the fast approaching mission.54
By July, the crew of Gemini XII was being assigned some rather precise objectives. In fact, the flight was soon extended to four days to give the crew time for experiments that depended on nighttime operations. Over the course of the program, mission planning had steadily progressed to expand manned space flight experience, but Gemini XII assumed a more conservative cast, as shown by a comparison of preliminary and final flight plans for the mission.
In July, for example, the primary objectives were rendezvous and docking, preferably in the second spacecraft orbit, and extravehicular activity with the AMU. Two of the secondary goals were repeats: rerendezvous from above (from Gemini IX-A) and a tethered vehicle exercise (from Gemini XI). Then came the decision to delete the AMU, and Mueller told Chuck Mathews that he also opposed the rerendezvous plan. Next, rendezvous and docking shifted from the second to the third spacecraft orbit (which had already been done). These changes, of course, affected the flight plan, delaying a final version. Mathews told MSC's senior staff as late as mid-September that the hardware would be ready for launch but that what would be done during the flight was still not firm. The final flight plan was not ready until 20 October. And it contained no surprises. Almost the only innovation was the non-spinning, gravity gradient mode of stationkeeping. But that was not really new, since Conrad and Gordon had tried it, without success, on Gemini XI.55 There was to be no trail-blazing on the final mission.
If, as Lovell said, "essentially Gemini XII didn't have a mission," it did have a theme - to pierce the mystery of working in space. The strain of EVA experienced so severely by Cernan and Gordon not only clouded Gemini but raised doubts for Apollo. The lack of understanding of the difficulty emerged as a pressing concern that did much to shape Gemini's final flight.  To increase the chances for success on Gemini XII, NASA now arranged to study in a careful and systematic way the basic features of EVA.56
Training and restraints for EVA underwent significant changes. In prior training, the crews had used zero-g aircraft flights to get the feel of weightlessness and to devise techniques for working. But experience had shown that this kind of training was useful in a very limited way, mainly for practice in getting into or out of the spacecraft. Pilots had to move fast and brace themselves before the airplane finished the Keplerian trajectory with its high-g pullout. In space, they found that everything had to be done slowly and deliberately. Nor could the kind of fatigue that Cernan and Gordon had suffered in space be assessed in zero-g flights, because the delay between successive parabolas imposed a rest period. Almost a full day had to be spent in the aircraft to accumulate 15 minutes of weightlessness.
But in mid-1966, underwater simulation had been advanced to meet these shortcomings. Moving in a viscous and buoyant fluid was very much like moving against the restraints of a pressurized suit in a weightless vacuum. Aldrin could thus get a more accurate sense of the time and physical effort required for a task on the workstands (called "busy boxes") during flight. Since the zero-g aircraft exercise did give him the feel of weightlessness, however, Aldrin continued that training also.57
On each of the last three missions, the pilots who went outside had complained that they needed more help in body positioning. Each spacecraft carried more restraints than the one before. The 9 restraints on Gemini IX-A had become 44 on Gemini XII. One helpful innovation was a waist tether that allowed the pilot to retrieve packages, turn wrenches with considerable torque, and attach the vehicle tether without undue stress. Other new features were handrails, handholds, and rings for hooking Aldrin's restraining belt to various places on the spacecraft and target vehicle. At last, an EVA pilot had all the help he would need for performing a great variety of tasks, some of considerable complexity.
After Gemini IX-A, MSC's Crew Systems Division puzzled over Cernan's fatigue. Collins' success in Gemini X suggested that the order in which he did his extravehicular tasks might have made them easier. Collins had done a standup EVA and then closed the hatch and rested before leaving the spacecraft. After Gordon had to come in early on Gemini XI, GPO decided that Aldrin would begin with a standup exercise and then go on to more strenuous activity.58
Although flight planning was the hardest part of getting ready for the final Gemini mission, hardware could have been a monumental problem - spares were becoming scarce. This danger had been foreseen and reasonable provisions made long before the scheduled launch  date, but program officials could not help being jumpy, fearing they would be unable to replace a part that had suddenly gone awry.
When the Gemini IX Agena had fallen into the Atlantic Ocean, Gemini XII was threatened with a major hardware shortage - an Agena and an Atlas to launch it. Replacing the Agena was no real problem. Lockheed's first production model, 5001, used for development testing at the Cape, had already been sent back to the Sunnyvale plant for refurbishment. Now it was simply a matter of tailoring it to the Gemini XII mission.59
Finding a new Atlas was not so easy. General Dynamics did not keep a stockpile of Atlases on the assumption that someone would come along and buy them. GPO would have to find one that had been intended for some other program. When a Lunar Orbiter flight was delayed in May, it freed an Atlas that GPO might acquire. And when Mueller approved the purchase of a replacement vehicle on 1 June, MSC was already negotiating for an Atlas at Vandenberg Air Force Base in California. But this was not the standard vehicle Gemini had been using; it was the first of a new series with some features that had never been tested in flight. Langley Research Center, in charge of the Orbiter payload, was persuaded to turn its Atlas over to Gemini in exchange for the one in California. Langley's Orbiter Atlas had only nine variances from the Gemini version, and the trade eased the minds of the MSC program engineers. By the end of September, the new Atlas waited on pad 14 at Cape Kennedy for its call to action.60
* The membership remained the same from the beginning: Elms, Edgar Cortright, Major General Vincent Huston, and Charles Mathews.
48 George M. Lows written report of the trip, in journal form, provides some interesting insight and commentary about behind-the-scene and in-the-scene activities involved in a goodwill tour. His comments on the leaders of the countries (in which they met the president or acting president, cabinet members, legislators, governors, and mayors) indicate that these officials were surprisingly familiar with the details of Gemini. Low said the press of South America also seemed to be well informed about the program. Low, "Latin American Tour with Astronauts Armstrong and Gordon, October 7-11, 1966," 16 Nov. 1966.
49 "Gemini XII Technical Debriefing," 22 Nov. 1966, p. 428; James A. Lovell, Jr., interview, Houston, 15 April 1967.
50 Funk letter, 12 July 1966; letter, Gilruth to Funk, GS-64161, 26 July 1966; Elms, conversation with Grimwood, 14 Oct. 1968; Elms interview.
51 Elms, "Third Interim Report, Gemini Mission Review Board, October 25, 1966"; memo, Samuel H. Hubbard to Chairman [Elms], "Gemini Mission Review Board Meeting of September 13, 1966," 18 Oct. 1966.
52 Elms, "Third Interim Report;" memo, Elms to Assoc. Adm., OMSF, "Review of Gemini XII Mission Elements," 23 Sept. 1966.
53 Elms memo, 23 Sept. 1966; letter, Mueller to Ferguson, 30 Sept. 1966.
54 TWX, Mathews to Langley Research Center, Attn: Floyd L. Thompson, Otto F. Trout, Jr., and Robert R. Moore, Jr., GV-12504, 1 Sept. 1966; TWX, Edwards to MSC, Attn: Mathews, "Experiment Deletion from Gemini XII," MGS-522, 27 Sept. 1966; datafax transmission, William J. O'Donnell to MSC, Attn: Howard I. Gibbons, MSFC, Attn: Joe M. Jones, and KSC, Attn: John W. King, "Draft release #3," 27 Sept. 1966; letter, Mathews to McDonogh School, Attn: Robert L. Lamborn, GV-66555, 9 Nov. 1966; "Gemini Program Mission Report, Gemini XII," MSC-G-R-67-1, January 1967, p. 12-5; Mattingly letter, 5 Oct. 1970.
55 "Gemini Program Mission Directive," p. A-12-1, Change 4; memo, Gill to dist., "Summary Minutes of 6th Inflight Experiments Meeting, 66-3, held at NASA Headquarters, Washington, D.C., April 28, 1966, April 29, 1966," 16 June 1966, p. 4; Lee, "Minutes of Senior Staff Meeting, August 12, 1966," p. 3; TWX, Mathews to McDonnell, Attn: Burke, "Contract NAS 9-170, Gemini Configuration Control Board Meeting Number 116, August 8, 1966," GV-12492, 11 Aug. 1966; Youngblood, "Minutes of Senior Staff Meeting, September 30, 1966," p. 3; memo, Mathews to NASA Hq., Attn: Schneider, "Gemini XII Mission Priorities," GV-66519, 7 Oct. 1966; Youngblood, "Minutes of Senior Staff Meeting, September 16, 1966,"p. 4; E[lvin] B. Pippert, Jr., and T[ommy] W. Holloway, "Gemini XII Flight Plan," Final, 20 Oct. 1966; Meyer, notes on GPO staff meeting, 20 Oct. 1966, p. I; NASA Release No. 66-272, "Project: Gemini 12," press kit, 28 Oct. 1966, pp. 1, 11.
56 TWX, Mueller to MSC, Attn: Gilruth, "Gemini XII Flight Plan," M/473, 26 Sept. 1966; TWX, Gilruth to NASA Hq., Attn: Mueller, "Gemini Extravehicular Reporting," GP-7658, 4 Oct.1966; "Gemini XII Debriefing," p. 428; Elms memo, 23 Sept. 1966.
57 [Warren J. North], "EVA Position Paper," n.d., pp. 2, 3; Schultz et al., "Extravehicular Training and Simulation," pp. 7-23, -35; Reginald M. Machell et al., "Summary of Gemini Extravehicular Activity," in Gemini Summary Conference, pp. 139-46; Gemini 11 press kit, p. 22.
58 David C. Schultz et al., "Body Positioning and Restraints during Extravehicular Activity," in Gemini Summary Conference, pp. 79, 83-84, 85, 86-87; TWX, Mathews to McDonnell, Attn: Burke, "Contract NAS 9-170, Gemini, Action Items Resulting from Spacecraft 12 Flight Readiness Review," GP-7679, 31 Oct. 1966; Bell interview. TWXs, Mathews to SSD, Attn: Col. Alfred J. Gardner, GV-12384, 14 March, and GP-7509, 1 April 1966; TWX, Mathews to SSD, Attn: Conkling, "Major Hardware Shipment for Gemini XII Mission," GA-6023, 11 Aug. 1966; "Abstract of Meeting on Atlas/ Agena Coordination, August 24, 1966," 14 Sept. 1966; James M. Grimwood and Barton C. Hacker, Project Gemini Technology and Operations: A Chronology, NASA SP-4002 (Washington, 1969), p. 279.
59 TWXs, Mathews to SSD, Attn: Col. Alfred J. Gardner, GV-12384, 14 March, and GP-7509, 1 April 1966; TWX, Mathews to SSD, Attn: Conkling, "Major Hardware Shipment for Gemini XII Mission," GA-6023, 11 Aug. 1966; "Abstract of Meeting on Atlas/Agena Coordination, August 24, 1966." 14 Sept. 1966; James M. Grimwood and Barton C. Hacker, Project Gemini Technology and Operations: A Chronology, NASA SP-4002 (Washington, 1969), p. 279.
60 Meyer notes, May 18, 1966, p. 1; TWX, Mathews to NASA Hq., Attn: Day, "Procurement of an Atlas Launch Vehicle for Gemini XII Mission," GP-7582, 14 June 1966; TWX, Mathews to SSD, Attn: Gardner, GV-12368, 8 March 1966; TWX, Mathews to SSD, Attn: Gardner, "Disadvantages of Flying Atlas 5307 in Its Planned Configuration," GP-7610, 8 July 1966; TWX, Mathews to SSD, Attn: Gardner, "Atlas Vehicle for Gemini XII," GV-12468, 19 July 1966; TWX, Mathews to Lewis Research Center, Attn: Edward F. Baehr and Henry W. Plohr, "Atlas Vehicle for Gemini XII," GV-12469, 18 July 1966; Lee, "Minutes of Senior Staff Meeting, July 8, 1966," p. 4.