When the RAF expansion schemes were inaugurated in the mid-1930s, many squadrons were reformed, including No.115 which reformed out of No.38 Squadron's 'B' Flight at Marham on 5 June 1937. At first it had to borrow No.38's Fairey Hendon night bombers, but within two months it had a full establishment of its own Handley Page Harrows.
Despite interruptions, No. 115 became operational within a year, forming part of No. 3 Group's expanding bomber force. The Harrow, however, would have been no use had war come and at the end of March 1939 the squadron began to re-equip with Vickers Wellingtons, with which it trained at great intensity because war was imminent. By the outbreak of World War 2 on 3 September the squadron was again operational.
Its first operation was flown on 8 October to attack the German fleet off Norway, but no ships were sighted. No. 115's first successful raid was flown on 3 December, when German shipping at Heligoland was bombed. The bombing force was attacked by enemy fighters but the squadron lost no aircraft. This was the end of daylight raids apart from North Sea sweeps which were carried out on an occasional basis. At night the squadron went on 'Nickel' raids (dropping pamphlets) until March 1940, when it flew north to attack German shipping taking part in the Norwegian invasion, Bergen and Stavanger being the main targets; during these raids the squadron lost its first aircraft to enemy fire.
With the German invasion of Belgium and the Netherlands, the squadron began its long association with the Ruhr, bombing by night, principally attacking oil refineries and rail installations. As the position in France grew worse, No. 115 switched to tactical bombing to support the armies in France. When this campaign was over No. 115 returned to the attack on Germany and its industry, striking deeper and deeper into the Reich and reaching Berlin on 28 August 1940. In September the unit was diverted to bombing invasion barges in the Channel ports. The squadron was slowly learning the do's and don'ts of night bombing, suffering casualties on the way and finding that the main problem over a blacked-out country was finding its way about. Bomber Command was now the only means of striking back at Germany, so the bomber offensive was top priority and No.115 was carrying out raids night after night.
To help with the navigational problems which the bomber crews were experiencing a new radar navaid had been developed, code-named 'Gee', a number of sets being fitted to No.115 Squadron's Wellingtons in January 1941 for tests. Development took a lengthy time, but in August 1941 the squadron began to use the aid operationally, 'Gee' helping it to find and return from Monchengladbach. More raids followed, and the benefit of 'Gee' became more clearly apparent. These were just part and parcel of the continuous offensive that the continuous offensive that the squadron was flying all through 1941, many of its raids being against German ports to immobilize the German battle-cruisers and disrupt the U-boat bases on the French Atlantic coast.
In November 1941 the Wellington Mk III replaced the Mk I, giving the squadron greater power and more firepower in the rear turret. 'Gee' was now a standard fitting and improving the quality of the raids. Another new method to enhance the effect of the raids was carried out by No. 115 and other No. 3 Group squadrons in March 1942 when flares were dropped to illuminate the targets for the main force of bombers. This was soon followed by the first 'thousand-bomber' raid, against Cologne on 30 May. In September the squadron foresook its traditional base at Marham for Mildenhall, moving soon after to a satellite at East Wretham. With the long nights of winter the squadron now set out for Italian targets, Turin being the first in November 1942.
By now the Wellington was becoming outdated for the battle of Germany, so the squadron found itself largely relegated to minelaying in the first few months of 1943. Then in March came Avro Lancasters, and to the squadron's surprise they were the Hercules-engined version, the Mk II. Unfortunately this version had a low ceiling and No.115 was the first unit to be fully operational with the type. It was found that on each raid at least one aircraft was lost, and the losses began mounting seriously during the summer. The Ruhr was again the principal area of operation and the crews found that they were increasingly being attacked by German night-fighters, not only over Germany but in the circuit when they returned to base. In November 1943 the squadron settled at Witchford for the rest of the war.
In March 1944 the Hercules-engined Lancasters began to be replaced by Merlin-engined Mk Is and Mk IIIs enabling the squadron to have greater flexibility in its operations. It was now increasingly involved in the softening up of France for the invasion, and also in the desperate attempt to eliminate as many as possible of the V-1 sites in France and Belgium before they could be used to annihilate south east England. Many of its raids were now by daylight over France, but over Germany the squadron maintained its night offensive, concentrating on this once the armies were well established in France. So during the winter of 1944-5 it took part in many of the devastating raids that were a feature of the last months of the war. Its last raid was on 24 April on rail marshalling yards, and the squadron ended the war with 5,392 sorties made. After the end of the hostilities it flew food-dropping sorties over the Netherlands, followed by flights repatriating POWs from Germany and Italy.
The squadron was now allocated to 'Tiger Force', a bomber force being built up to go and attack the Japanese mainland. It received Lancasters modified for Far East use, but before the squadron could go east the war was over. Instead, the squadron was gradually reduced in size and servicing became difficult as a result of the shortage of ground crew due to demobilization. However, No.115 was not, like so many squadrons, disbanded. The next few years were dismal, but in 1948 things began to pick up as the RAF had settled into its permanent peacetime set-up. Overseas flights were made to Egypt and the Sudan on Operation 'Sunray', and slowly the intensity of UK-based exercises increased. The Berlin Airlift and then the attack on Korea made everyone realize that there was to be no real peace. In September 1949 the Lancasters at last were replaced by Avro Lincolns, but this was only a temporary measure. There was a new task for No.115 Squadron.
In March 1950 No. 115's crews were sent to the USA to train on the American Boeing B-29 Super-fortress, of which 87 were to be supplied to the RAF to serve until the British jet bombers were in service. No.115 Squadron was the first to receive these Washington bombers, bringing them back to the United Kingdom and Marham, its original base, on 13 June 1950. Now it had a busy task to work up to operational strength, participating in air defence exercises and sending one aircraft to the RAF display that year at Famborough. In 1951 and 1952 the squadron was part of the forefront of Bomber Command and was fully active in all exercises, also deploying to Malta and developing radar bombing techniques operationally. The squadron was fully represented in the RAF Review for Her Majesty the Queen at Odiham in 1953, with one aircraft in the static line-up and the rest of the squadron in the massed flypast. It was in that year that No. 115 won the Laurence Minot Bombing Trophy.
The following year No.115 converted to English Electric Canberras, along with the other Marham squadrons. It took a little while to become accustomed to the vast increase in performance and to learn the new techniques required. That year the squadron had an unique task flying scientists to observe the eclipse of the sun. The following year the squadron took part in overseas flights and also won the Efficiency Trophy. Similar flights were flown in 1956, and in that autumn No.115 was on standby to support the Canberra squadrons operating in the Suez campaign. It soldiered on into 1957, being disbanded at Marham on 1 June 1957.
On 21 August 1958 No. 116 Squadron at Watton was re-numbered No.115 Squadron. The squadron now had a completely different role. It was part of No. 90 Signals Group and its task was somewhat prosaic but vital, that of calibrating from the air all radio and radar installations at RAF airfields. Later in the year it moved to Tangmere, where it remained for five years on this task and also took part in calibrating ships' installations. It also flew a few Vickers Valettas for a year or two, during which time it was further tasked with medical evacuation duties. At the end of the five years, No. 115 returned to Watton and three years later was presented with its standard.
In 1968 the squadron re-equipped with Hawker Siddeley Argosy E.Mk 1s and with these it moved to Cottesmore, retaining some Vickers Varsities for another 18 months. It was one of these latter that flew the last 'Gee' checking sortie, so the squadron claims to be the first and last operator of 'Gee'. Now the calibration duties were extended as far as the Far East Air Force, and no.115s aircraft were to be seen wherever there were RAF bases. It also experimented, in 1972, with using its nose radar as a shipping search device, thus giving it a possible maritime commitment. The task carried on at Cottesmore until 1976, when the squadron moved to Brize Norton. Once moved the Argosy was swiftly replaced by the Hawker Siddeley Andover E.Mk 3, with which the squadron has carried on the calibration tasks up to the present day, moving to Benson in January 1983.