Glenn L. Martin began manufacturing aircraft in the early days of aviation at the beginning of the 20th century and went on to become one of the leading military airplane manufacturers in the United States. He retained control of the company for 40 years, hiring skilled engineers along the way, including some who would establish their own successful aircraft companies—Donald Douglas, William Boeing, and James McDonnell among them.

Martin established the Glenn L. Martin Aircraft Company in Santa Ana, California, in 1912. The first planes that he built for the Army Signal Corps were trainers—designated the Model TT—using the design services of the newly hired Donald Douglas. After delivery of the final TTs in early 1917 and a brief stint as the Wright-Martin Company, Martin closed his California factory and moved to Cleveland, Ohio, where he established a new Glenn L. Martin Aircraft Company.

In early 1918, the U.S. Army ordered the MB-1 from Martin, the first American bomber the Army purchased, replacing the larger and slower Handley-Page and Caproni aircraft. Douglas designed the airframe, which was the first built around the new U.S.-designed 400-horsepower Liberty engine. The first MB-1, designated the GMB (Glenn Martin Bomber), began flying on August 17, 1918, and delivery of the ten aircraft began in October, too late to serve in the war.

When the war ended, aircraft orders stopped. Some small orders from the Post Office and the Navy kept Martin in business until June 1920, when the Army ordered the MB-2. Similar to the MB-1, the prototype bomber was so successful that 130 were ordered. However, aircraft designs were considered public property, and government policy was to solicit competitive bids for its aircraft. Martin's bid for the MB-2 was higher than other bids, and the Army ended up ordering most of the aircraft from Curtiss, L-W-F Engineering, and Aeromarine using Martin's design. The MB-2 was best known for the 1921 bombing tests of German warships under the command of Brig. Gen. Billy Mitchell that proved the feasibility of bombing naval vessels from the air.

In spite of the success of the MB-2, Martin could barely keep afloat, and the company shrank from almost 400 to just 90 employees. Only a Navy order of four experimental aircraft between 1922 and 1924 kept the company going. One, the MO-1, an all-metal gun-spotting seaplane, had a fuselage framed in welded steel and wings framed in an aluminium alloy. The only wood in the structure was in the engine mount, where it was used to absorb vibration.

The company's fortunes improved in 1924 when Martin underbid Curtiss on a contract for production of a Curtiss scout bomber. The Navy purchased 360 SC-1s between 1924 and 1930—302 from Martin—and then 102 more with the large Pratt and Whitney R-1690 Hornet radial engine. By 1928, Martin's workforce had grown to more than 1,000. At this point, Martin sold both the factory and the designs to Detroit Aircraft, which kept producing the aircraft under its subsidiary, the Great Lakes Aircraft Company.

When Martin sold his Cleveland plant in 1929, he built a new plant near Baltimore in Middle River, Maryland. This plant was the first designed for metal aircraft construction and, during the 1930s, was regarded as the most modern factory in the United States.

By 1929, the Navy was beginning to give increasing attention to a possible confrontation with Japan in the Pacific. At the same time, its stock of flying boats was wearing out, and the Navy turned to Martin for replacement flying boats that would be equipped with the new top-secret Norden precision bombsight. The Navy ordered 25 Martin Model 117 PM-1 biplane flying boats in May 1929, another five the next month, all using the anti-corrosive aluminium alloy developed in the early 1920s by the Naval Aircraft Factory and the Aluminium Company of America (Alcoa)—called Alclad, and nine monoplane flying boats based on a Consolidated Aircraft design that was now public. Martin was able to underbid Consolidated on the monoplanes because it did not have to bear the development costs. However, even though Consolidated no longer owned the design, it refused to release its engineering drawings and data, and Martin was forced to measure and copy the aircraft. The aircraft were not delivered until May 1931.

Martin also improved the performance of the airfoil beginning with its Model 119 aircraft. It mounted the engine nacelles (the engine enclosure) into the leading edge of the wings in a smooth line instead of mounting them on struts, thus reducing vibration and drag.

Among the military aircraft in the interwar period, Martin's B-10 series—the 123, 139, and 166 models—stand out. Just as the MB series set the standard for bombers of the 1920s, the B-10 set the standard for the 1930s. It was the first of the modern all-metal monoplane bombers to be produced in quantity and the first to successfully apply the new technology that used a streamlined monocoque fuselage, variable-pitch propellers, thick metal wings with lift-enhancing flaps, integral fuel tanks, internal bomb storage, rotating gun turrets, and retractable landing gear. All crew positions were enclosed, and the bombardier used early versions of the Norden bombsight. With a top speed of 200 miles per hour (322 kilometres per hour), it was 50 percent faster than other biplane bombers and as fast as most of the fighters of the day.

The request for a design for an advanced bomber came in 1929. By the time Martin had developed the design, in 1932, the country was in the depths of the Depression, and winning the design competition was essential for Martin's survival. Martin's design of the B-10, put together with the help of the Air Corps Materiel Division, beat the competition from Boeing and Douglas.

In January 1933, the Army contracted with Martin for 48 planes, worth almost $2.5 million. In March 1933, President Franklin Roosevelt presented Glenn Martin with the Collier Trophy for aviation achievement. Martin accepted the award on behalf of "everyone who worked on the design and who helped rivet it together." But that wasn't good enough for the Air Corps Materiel Division, whose engineers insisted that Martin should have said he "owed it all" to them.

The B-10s had an unusual early use. In 1934, Postmaster General Jim Farley had cancelled all airmail contracts with private carriers and given the job of carrying the mail to the Army. The planes used were unsuited, the pilots were untrained, and fatalities were high. Farley put the big B-10s into service as mail carriers, vastly improving flight reliability and safety.

Airmail was returned to the private airmail carriers in May. In July and August, the Air Corps, in a show of strength, assembled ten B-10s and flew 7,360 miles (11,845 kilometres) from Washington, D.C. to Fairbanks, Alaska and back, under the command of Colonel Henry "Hap" Arnold. This project proved the feasibility of sending an aerial force to Alaska in an emergency and provided training for pilots flying over isolated areas.

After these successes, Martin assumed that it would be the only supplier of the B-10. But the Air Corps planned to solicit bids for the planes. Martin countered by requesting permission to export the planes to Soviet Russia, Brazil, and China. It was denied permission but it received an order worth $7.5 million spread over 1934 and 1935. In all, the orders that the Air Corps placed for B-10s between 1933 and1936 formed the largest purchase of bomber aircraft since World War I.

In 1935, the B-10 carried out the first army tests of the Navy's Norden precision bombsight. Its success confirmed strategists' expectations that daylight precision bombing could be effective even beyond the range of escort fighters. This helped stimulate the development of larger, longer-range bombers, particularly the Boeing B-17 Flying Fortress.

By 1936, the Air Corps was losing interest in the B-10 as a bomber and released the 139 model of the series for export. The company sold 189 planes abroad. The Dutch were the best customers, buying 120 planes to defend their Indonesian colonies. Foreign orders continued until 1939 and the planes flew in a number of military actions around the world. Some B-10s flew until the late 1940s in Turkey and in Siam (now Thailand) and perhaps even longer in Argentina.