The mission of Liberty Bell 7 was basically a repeat of Freedom 7 with the objective of corroborating the man-in-space concept. The notable improvements were a large viewing window, hand controls, and an explosively actuated side escape hatch which almost proved disastrous. While in the ocean off the Bahamas waiting to be picked up, the side hatch blew, causing the capsule to fill with water and sink, almost taking the Astronaut with it. A soaking wet Gus Grissom was safely rescued, although the Liberty Bell 7 sank to the bottom and was lost. Controversy remains to this day whether Gus blew the hatch prematurely or it was caused by some other unknown reason.

Among the improvements in spacecraft No. 11 for MR-4 was the explosive side hatch, which was requested by the astronaut corps. The original egress procedure had been to climb out through the antenna compartment and all of the astronauts found it hard to snake out the top of the frustum and cylinder.

There were two ways to activate the explosive egress hatch during recovery. About six to eight inches from the astronaut's right arm, as he lay in his couch, was a knobbed plunger. The pilot would remove a pin and press the plunger with a fist-force of five or six pounds, detonating the small explosive charge and blasting the hatch 25 feet away in a second. If the pin was in place, a fist-force of 40 pounds was required. A rescuer outside the capsule could blow open the hatch simply by removing a small panel from the fuselage side and pulling a lanyard. This complete explosive hatch weighed only 23 pounds.

The welcome new trapezoidal window assembly on spacecraft No. 11 replaced the two 10-inch side ports through which Shepard strained to see. The pilot now could look upward slightly and see directly outside. Visually the field covered 30 degrees in the horizontal plane and 33 degrees in the vertical. The outer pane was made of Vycor glass, .35-inch thick, and could withstand temperatures on the order of 1500 to 1800 degrees F. Three panels were bonded to make the inner pane, one a .17-inch- thick sheet of Vycor, the two others made of tempered glass.

The manual controls for the second manned flight incorporated the new rate stabilization control system. With it the astronaut could control the rate of spacecraft attitude movements by small turns of his hand controller rather than by jockeying the device to attain the desired position. This rate damping or rate augmentation system, like power steering on an automobile, gave finer and easier handling qualities and another redundant means of driving the pitch, yaw, and roll thrusters.

Grissom choose the name Liberty Bell 7 as the most appropriate call-sign for his bell-shaped capsule, because the name was to Americans almost synonymous with "freedom" and numerically symbolic of the continuous teamwork it represented. Someone had done Grissom the favour of painting a likeness of the crack in the original Liberty Bell on spacecraft No. 11.

Modifications made on Grissom's pressure suit reflected the experiences of Shepard's flight. Nylon-sealed ball-bearing rings were fitted at the glove connections to allow full rotation of the wrists while the suit was pressurized. On the chest of Grissom's suit was a convex mirror, called a "hero's medal" by the astronaut corps, that served simply to allow the pilot-observer camera to photograph instrument readings. Another welcome addition to the suit was a urine reservoir, fabricated the day before the flight. Although during his flight Grissom would find the contraption somewhat binding, it did work. Lastly, Grissom's helmet was equipped with new microphones that promised to filter out more noise and make transmission quality even better.

Grissom's flight plan was revised rapidly and altered substantially as a result of MR-3. Shepard had really been overloaded with activities during his five minutes of weightlessness. Now Grissom was given a chance to look through his new trapezoidal window to learn more about man's visual abilities in space. If he could recognize landmarks for flight reference, the pilot tasks for the Mercury orbital flights might be considerably simplified. Shepard had assumed manual control of only one axis of movement - yaw, pitch, or roll - at a time, whereas Grissom had instructions to assume complete manual control as soon as he could, to make three manoeuvres in about one minute instead of Shepard's 12 minutes, and then to spend as much time as possible making exterior observations.

Grissom was calm, and poised as he entered Liberty Bell 7. The count proceeded smoothly until 45 minutes before launch time, when a gantry technician discovered that one of the 70 hatch bolts was misaligned. A 30-minute hold was called, during which the McDonnell and STG supervisory engineers decided that the remaining 69 bolts were sufficient to hold and blow the hatch, so the misaligned bolt was not replaced. The countdown was resumed, but two more holds for minor reasons cost another hour's wait.

Grissom later admitted at the post-flight debriefing that he was "a bit scared" at lift-off, but he added that he soon gained confidence along with the g build-up. Hearing the engine roar at the pedestal, he thought that his elapsed-time clock had started late. Like Shepard, he was amazed at the smooth quality of the lift-off, but then he noticed gradually more severe vibrations, never violent enough to impair his vision.

At two minutes and 22 seconds after launch, the Redstone's Rocketdyne engine cut off after building a velocity of 6561 feet per second. Grissom had a strong sensation of tumbling during the transition from high to zero g, and, while he had become familiar with this sensation in centrifuge training, for a moment he lost his bearings.

A constant urge to look out the window made concentrating on his control tasks difficult. He told Shepard back in Mercury Control that the panorama of Earth's horizon, presenting an 800-mile arc at peak altitude, was fascinating. His instruments rated a poor second to the spectacle below.

Turning reluctantly to his dials and control stick, Grissom made a pitch movement change but was past his desired mark. He jockeyed the hand-controller stick for position, trying to damp out all oscillations, then made a yaw movement and went too far in that direction. By the time the proper attitude was attained, the short time allocated for these manoeuvres had been used, so he omitted the roll movement altogether. The manual controls impressed Grissom as very sluggish when compared to the Mercury procedures trainer. Then he switched to the new rate command control system and found perfect response, although fuel consumption was high.

After the pitch and yaw manoeuvres, Grissom made a roll-over movement so he could see the ground from his window. Some land beneath the clouds (later determined to be western Florida around the Apalachicola area) appeared in the hazy distance, but the pilot was unable to identify it. Suddenly Cape Canaveral came into view so clearly that Grissom found it hard to believe that his slant-range was over 150 miles. He saw Merritt Island, the Banana River, the Indian River, and what appeared to be a large airport runway. South of Cape Canaveral, he saw what he believed to be West Palm Beach.

With Liberty Bell 7 at an altitude of 118.26 miles, it was now time to position the spacecraft in its re-entry attitude. Grissom had initiated the retrorocket sequence and the capsule was arcing downward. His pulse reached 171 beats per minute. Retrofire gave him the distinct and peculiar feeling that he had reversed his backward flight through space and was actually moving face forward. As he plummeted downward, he saw what appeared to be two of the spent retrorockets pass across the periscope view after the retrorocket package had been jettisoned.

Re-entry presented no problem. Condensation and smoke trailed off the heat-shield at about 65,000 feet as Liberty Bell 7 plunged back into the atmosphere. The drogue parachute deployed on schedule at 21,000 feet. Main parachute deployment occurred at 12,300 feet, which was about 1,000 feet higher than the design nominal altitude. Watching the main chute unfurl, Grissom spotted a six-inch L-shaped tear and another two-inch puncture in the canopy. Although he worried about them, the holes grew no bigger and his rate of descent soon slowed to about 28 feet per second.

A "clunk" confirmed that the landing bag had dropped in preparation for impact. Grissom then removed his oxygen hose and opened his visor but deliberately left the suit ventilation hose attached. Impact was milder than he had expected, although the capsule heeled over in the water until Grissom was lying on his left side. He thought he was facing downward. The capsule gradually righted itself, and, as the window cleared the water, Grissom jettisoned the reserve parachute and activated the rescue aids switch. Liberty Bell 7 still appeared watertight, although it was rolling badly with the swells.

Preparing for recovery, he disconnected his helmet and checked himself for debarkation. The neck dam did not unroll easily; Grissom tinkered with his suit collar to ensure his buoyancy if he had to get out of the spacecraft quickly. Lieutenant James L. Lewis, pilot of the primary recovery helicopter, radioed Grissom to ask if he was ready for pickup. He replied that he wanted them to wait five minutes while he recorded his cockpit panel data. Using a grease pencil with the pressure suit gloves was awkward, and several times the suit ventilation caused the neck dam to balloon, but the pilot simply placed his finger between neck and dam to allow the air to escape.

After logging the panel data, Grissom asked the helicopters to begin the approach for pickup. He removed the pin from the hatch-cover detonator and lay back in the dry couch. "I was lying there, minding my own business," he said afterward, "when I heard a dull thud." The hatch cover blew away, and salt water swished into the capsule as it bobbed in the ocean. The third man to return from space was faced with the first serious emergency; Liberty Bell 7 was shipping water and sinking fast.

Grissom had difficulty recollecting his actions at this point, but he was certain that he had not touched the hatch-activation plunger. He doffed his helmet, grasped the instrument panel with his right hand, and scurried out the sloshing hatchway. Floating in the sea, he was thankful that he had unbuckled himself earlier from most of his harness, including the chest restraints. Otherwise he might not have been able to abandon ship.

Instead of turning his attention to Grissom, Lieutenant John Reinhard, co-pilot of the nearest recovery helicopter, completed his approach to the sinking spacecraft, as both he and Reinhard were intent on capsule recovery. This action was a conditioned reflex based on past training experience. While training off the Virginia beaches the helicopter pilots had noted that the astronauts seemed at home in and to enjoy the water. So Reinhard quickly clipped the high-frequency antenna as soon as the helicopter reached Liberty Bell 7. Throwing aside the antenna cutting device, Reinhard picked up the shepherd's hook recovery pole and carefully threaded the crook through the recovery loop on top of the capsule. By this time Lewis had lowered the helicopter to assist Reinhard in his task to a point that the chopper's three wheels were in the water. Liberty Bell 7 sank out of sight, but the pickup pole twanged as the attached cable went taut, indicating to the helicopter pilots that they had made their catch.

Reinhard immediately prepared to pass the floating astronaut the personnel hoist. But at that moment Lewis called a warning that a detector light had flashed on the instrument panel, indicating that metal chips were in the oil sump because of engine strain. Considering the implication of impending engine failure, Lewis told Reinhard to retract the personnel hoist while he called the second chopper to retrieve the pilot.

Meanwhile Grissom, having made certain that he was not snared by any lines, noticed that the primary helicopter was having trouble raising the submerged spacecraft. He swam back to the capsule to see if he could assist but found the cable properly attached. When he looked up for the personnel line, he saw the helicopter start to move away.

Suddenly Grissom realized that he was not riding as high in the water as he had been. All the time he had been in the water he kept feeling air escape through the neck dam. The more air he lost, the less buoyancy he had. Moreover, he had forgotten to secure his suit inlet valve. Swimming was becoming difficult, and now with the second helicopter moving in he found the rotor wash between the two aircraft was making swimming more difficult. Bobbing under the waves, Grissom was scared, angry, and looking for a swimmer from one of the helicopters to help him tread water.

A "horse-collar" lifeline was tossed to Grissom, who immediately wrapped himself into the sling backwards. Lack of orthodoxy mattered little to Grissom now, for he was on his way to the safety of the helicopter, even though swells dunked him twice more before he got aboard. His first thought was to get a life preserver on. Grissom had been either swimming or floating for a period of only four or five minutes, "although it seemed like an eternity to me," as he said afterward.

Obviously one of the major problems to be explained and resolved following the flight of Liberty Bell 7 was the malfunction of the explosive egress hatch. Before the mission, environmental tests were conducted to qualify the hatch and igniter assembly. Although the tests had been run with the pin installed, conditions had been severe. The component had been subjected to low and high temperature ranges, a 100-g shock force, and salt-spray and water-immersion tests. After MR-4, the Space Task Group established a committee that included Astronaut Schirra to study the hatch problem. Tests were conducted in an environment even more severe than that used by the manufacturer, but no premature explosions occurred. Studies were made of individuals operating the panel switches on the side nearest the actuator; the clearance margin appeared to be adequate. According to Schirra, "There was only a very remote possibility that the plunger could have been actuated inadvertently by the pilot."

The mystery of Grissom's hatch was never solved to everyone's satisfaction. Among the favourite hypotheses were that the exterior lanyard might have become entangled with the landing bag straps; that the ring seal might have been omitted on the detonation plunger, reducing the pressure necessary to actuate it; or that static electricity generated by the helicopter had fired the hatch cover. But with the spacecraft and its onboard evidence lying 15,000 feet down on the bottom of the Atlantic Ocean, it was impossible to determine the true cause. Grissom would be the only astronaut who used the hatch without receiving a slight hand injury. As he later reminded Glenn, Schirra, and Cooper, this helped prove he had not touched his hatch plunger. Did Gus blow the hatch? Data collected from other Mercury astronauts say no. Every other astronaut that blew the hatch manually got bruised or cut. Gus did not.

Grissom expressed his opinion in an interview on April 12, 1965, that he believed the premature hatch explosion was caused by the exterior lanyard being loose. At that time it was held in place by only one screw. Subsequently a better method of securing the lanyard was effected.