2nd Lt. Elwood R. Quesada, an engineer of the U.S. Army Air Corps stationed at Bolling Field in Washington, D.C., developed a plan with a U.S. Marine Corps aviator from Anacostia Naval Air Station to break the Belgians' record. The plan was reviewed by Capt. Ira C. Eaker, an aide to Assistant Secretary of War for Air F. Trubee Davison. Eaker took it to Maj. Gen. James E. Fechet, Chief of the United States Army Air Corps. Both Fechet and Davison approved the project on the condition that it demonstrate a military application and not just as a publicity stunt. Overall command of the project was given to Major Carl A. Spaatz (who then spelled his named "Spatz"), the Assistant G-3 for Training and Operations in Fechet's office.
A 45-gallon tank was used to provide engine oil to the three motors, replenished by inflight deliveries of 5-gallon cans of Pennzoil triple-extra-heavy lowered on slings. A copper tubing system was installed in an attempt to adequately lubricate the rocker arms of the engines inflight. Doorways were cut on each side of the cockpit and catwalks built on the wings to enable Hooe to access the engines for emergency maintenance. To reduce propeller noise, the two wing engines were mounted with Westinghouse twin-blade Micarta propellers, while the nose engine used a Standard three-blade steel propeller.
As word of the project spread, its members were continually being asked how long they expected to remain aloft. Their responses were generally to the effect: "That is the question." A large question mark was painted on each side of the fuselage to provoke interest in the endurance flight.
To deliver the fuel, two Douglas C-1 single-engine transports were modified, s/n 25-428 as Refueling Airplane No. 1 and s/n 25-432 as Refueling Airplane No. 2. The bi-plane C-1s were evolved from the Douglas World Cruiser's design, with the pilots side-by-side in an open cockpit forward of the wing. Each was modified by installing two 150-gallon tanks in its cargo compartment attached to a lead-weighted 50-foot length of 2.5 inch fire hose. The nozzle of the hose had a quick-closing valve on the tanker's end and was tightly wrapped with copper wire, one end of which could be attached to a corresponding copper plate mounted in Question Mark to ground the hose. The C-1's would each carry a third crewman in the cargo compartment to reel out the hose or lower a supply rope, and to work the shutoff valve.
Van Nuys was chosen over an existing dirt strip airfield, Mines Field, located at El Segundo, because the weather in Van Nuys was considered more reliable, particularly in regard to temperature inversions and smog. Metropolitan was also an operational facility while Mines Field had just been procured by the City of Los Angeles for use as a commercial airport. The project arrived there in December 1928 to begin preparations for the flight, with Capt. Hugh M. Elmendorf in charge of logistics and maintenance.
Because of weight considerations and the unreliability of radios, none was installed in the Question Mark. All communications between the aircraft or between Question Mark and the ground had to be accomplished using flags, flares, flashlights, weighted message bags, notes tied to the supply lines, or messages written in chalk on the fuselages of PW-9D fighters, painted black and nicknamed "blackboard planes". (One such message written on the side of a 95th Pursuit Squadron is externally linked below.)
Four pilots of the 95th Pursuit Squadron, based at Rockwell Field, flew the PW-9 "blackboard planes": 1st Lt. Archie F. Roth, and 2nd Lts. Homer W. Kiefer, Norman H. Ives, and Roger V. Williams.
Less than an hour later Lt. Moon completed the first refueling over Van Nuys. During refuelings, Eaker and Halverson manned the controls, Spaatz and Quesada supervised the fuel exchange, and Hooe operated a "wobble" pump. The C-1 approached the Question Mark from above and behind, maintaining 20 to 30 feet of vertical separation, until in a position slightly ahead of the C-2. Both aircraft stabilized in level flight at 80mph and the hose was reeled out. Maj. Spaatz climbed on a platform below the open hatch, and wearing rain gear and goggles for protection against fuel spills, grounded the hose and then placed it in a receptacle mounted in the upper fuselage.
Made from a bucket with a sloped floor, the receptacle had connections to the two extra fuel tanks, and at Spaatz's signal Lt. Salter opened the valve. Fuel flowed by gravity into the bucket at 75 gallons per minute and then into the tanks, where it was then pumped by hand into the wing tanks by Sgt. Hooe. Food, mail, tools, spare parts and other supplies were also passed by rope in the same fashion.
During the first night-time refueling, Spaatz was drenched with fuel when turbulence caused the hose to pull out of the receptacle. Fearing that chemical burns from the gasoline might force him to parachute from the airplane to seek medical treatment, Spaatz ordered Eaker to continue the flight regardless. However Spaatz shed all his clothing and was wiped off with oil-soaked rags. Although he directed at least one refueling without his clothing, replacements were soon delivered. Quesada was briefly overcome by the same accident but quickly revived. Spaatz experienced two other fuel spills without injury, using oil to wipe his skin and zinc oxide to protect his eyes. Fog, turbulence, and darkness altered the refueling schedule, shortening some contacts and delaying others. On six occasions the Question mark was forced away from its flight track to refuel, once over Oceanside and five times over El Centro. Maintaining contact formation became more difficult as the weight of the planes changed during transfer, especially since the refueling pilot could not observe the Question Mark. Capt. Hoyt developed a system whereby Lt. Woodring tugged on a string tied to the pilot's arm if the C-1's speed was excessive. Early in the flight a window blew out of the C-2's cabin, but a replacement was eventually hauled up and installed by Sgt. Hooe.
On the afternoon of January 7, the left wing engine quit. Hooe went out on the catwalk to attempt repairs, immobilizing the windmilling propeller with a rubber hook. Eaker increased throttle on the remaining two engines to maintain flight while repairs were attempted, and they too began to strain. The plane lost altitude from 5,000 to 2,550 feet before Hooe was called back inside and the decision made to land.
The Question Mark landed under power at Metropolitan Airport at 2:06 p.m., 150 hours, 40 minutes, and 14 seconds after takeoff. The left engine had seized because of a pushrod failure, and the others all suffered severe rocker arm wear.
All five crew members were decorated with the Distinguished Flying Cross at a ceremony held at Bolling Field on January 29. The crews of the tankers, on the other hand, went unrecognized. Eventually all six received letters of commendation for their participation, but it was 47 years before their vital role in the operation was recognized with decorations. By then only Hoyt and Hopkins remained living, but both personally received Distinguished Flying Crosses on May 26, 1976.
The Air Corps followed up the flight of the Question Mark with a mission to demonstrate its applicability in combat. On May 21, 1929, during annual maneuvers, a Keystone LB-7 piloted by Lt. Moon took off from Fairfield Air Depot in Dayton, Ohio, on a simulated mission to New York City via Washington, D.C. Plans were for the bomber to be refueled in flight several times, drop a flash bomb over New York harbor, then return to Dayton non-stop, again by way of Washington. Moon had as a member of his five-man crew 1st Lt. John Paul Richter, who had been a hose handler on the first-ever refueling aerial refueling mission on May 28, 1923. The C-1 tanker employed to refuel the LB-7 was flown by Capt. Hoyt and two enlisted men. While it performed a premature air refueling enroute from Dayton to Washington, icing forced the tanker to land in Uniontown, Pennsylvania, where it got stuck in mud. After flying to New York, the LB-7 was forced to land at Bolling Field. The next day the tanker joined the bomber and both flew to New York, where they made a public demonstration of air refueling and four dry runs.
Of the 15 Army aviators involved in the project, six later became general officers. Spaatz, Eaker and Quesada played important roles in the United States Army Air Forces during World War II. Spaatz rose to commanding general of the Army Air Forces and became the first Chief of Staff of the United States Air Force. Eaker commanded the Eighth and Mediterranean Allied Air Forces. Quesada commanded the IX Tactical Air Command in France. Strickland, Hoyt and Hopkins all became brigadier generals in the United States Air Force, and the Brigadier General Ross G. Hoyt Award is issued annually for the best air refueling crew in the Air Force. Halverson, though he rose only to colonel, led the HAL-PRO ("Halverson Project") detachment, 12 B-24 Liberators that bombed the Ploieşti oil refineries in 1942, and was the first commander of the Tenth Air Force. Moon, a bomber pilot, became an influential member of the "Bomber Mafia" at the Air Corps Tactical School from 1933 to 1936, but died before the start of World War II.
The Question Mark was re-engined with 300-horsepower Wright R-975 engines in 1931, and redesignated as a "C-7". It served out its service life as the transport airplane for the 22nd Observation Squadron at Pope Field, North Carolina.