Derek Beeston joined the Royal Marines on 2 September 1935 in 226 Squad and was awarded the King's Badge. He served in HMS Glasgow before being promoted to Acting Corporal in March 1938 and confirmed in the rank in May 1939 before serving briefly in HMS Effingham, a Hawkins class heavy cruiser. He volunteered for flying and commenced training on No 6 Naval Pilots' Course in

Sydenham, Belfast. He was transferred to the RN on probation as an Acting Leading Seaman in August 1939, before progressing to No 1 FTS, Netheravon. During his training at Netheravon he had one serious incident when he executed a 'wheels up' forced landing in a Fairey Battle, fortunately without injury to himself, although the aircraft was badly damaged.

He completed his flying training on 21 April 1940 and his transfer to the RN was confirmed in the rank of Acting Petty Officer Airman ; FAA official number FX 82759.

After his basic training Beeston qualified as a seaplane pilot in 751 Squadron, initially at RNAS Ford. However, the squadron was moved from Ford to RNAS Yeovilton in May 1940 after the airfield was bombed. Beeston was then transferred again to RNAS Arbroath in August 1940 and finally to 764 Squadron based at Lee-on-Solent. The squadron provided an advanced seaplane conversion course, each course culminating in catapult exercises from HMS Pegasus. After qualifying Beeston was appointed successively to HMSs Cumberland, a County class heavy cruiser, and Sheffield, a Town class cruiser, as the Walrus pilot; both these ships were employed escorting Arctic Convoys. He then served at RNASs Arbroath and Machrihanish. 740 Squadron at RNAS Machrihanish was a communications squadron that also contained a Swordfish Torpedo Training Flight. The squadron flew a variety of types including Sea Otters, Swordfish, Dominies, Ansons and Oxfords. From Machrihanish Beeston was appointed to RNAS Piarco, Trinidad, for instructional duties at the Observer Training School, by then having been promoted to Chief Petty Officer.

In late 1945, after the end of WW2, Beeston returned from Trinidad and after a series of short flying appointments and conversions was promoted to Warrant Flying Officer and in that rank served in HMS Theseus as the Hangar Control and Safety Equipment Officer. This appointment coincided with the outbreak of the Korean war. After returning to the UK he undertook a series of courses, was commissioned and appointed to HMS Zeebrugge in January 1952 in a non-flying appointment to gain his watchkeeping certificate. Zeebrugge was an LST converted to be an accommodation ship and during Beeston's tour was engaged in Operation HURRICANE, the atom bomb tests on one of the Montebello Islands off the North West Coast of Australia.

Beeston returned to flying duties in late 1953 for refresher flying before taking up an instructional appointment at the School of Aircraft Handling. During this tour, in 1954, it is alleged that during an Admiral's inspection of HMS Siskin the Admiral, who had clearly been briefed beforehand, said to Beeston: “I believe you are a King's Badgeman. You must wear your badge”. According to the Globe & Laurel (1952, page 76) Beeston, at least for a short time, became the only RN officer to wear the King's Badge. However, it is suspected that not all his senior officers were so understanding because, according to photographic evidence, Beeston was not wearing King's Badge in later appointments.

Beeston flew thirteen aircraft types in the course of his career. He then trained as an Air Traffic Control Officer in 1956 and completed one tour as a controller at RNAS Eglinton, Co. Londonderry, before retiring as a Lieutenant Commander in 1959. He then became the licensee of two public houses before emigrating to Australia in 1968.