He 111 H-0 were pre-production aircraft with Junkers Jumo 211A-1 engines which led to the standard H-1 production models with improved radio kits. The H-2 was given improved defensive machine gun armament and H-3 followed with Junkers Jumo 211 A-3 engines and five machine guns with provision for cannon support as well. H-4 took on Junkers Jumo 211D series engines and featured bomb racks under the wings as well as support for torpedo dropping. H-5 carried all of its ordnance load externally with its bomb bay now reserved for fuel - thus allowing for drastically increased operational ranges. H-6 was a dedicated torpedo bomber form with combination machine gun/cannon armament. H-7 served in the night bomber role and lost some of its defensive armament while having additional armoring. H-8 were H-3 and H-5 models with barrage balloon-cutting equipment installed. The H-8/R2 were H-8 models relegated to towing duties. H-9 was built from the H-6 model with balloon-cutting equipment installed. Other H-model forms introduced slight variations on the base design - some with more guns (H-20) and others used solely as infantry transport (H-20/R1). H-20/R3 served in the night bomber role and H-20/R4 was given extensive external bomb rack equipment. H-22 served as an air-launch platform for V-1 "Buzz Bomb" terror weapons as the war moved on. He 111R was a high altitude bomber program.
The typical He 111 form (H-6) utilized a crew of five made up of the pilot, nose gunner who doubled as the bombardier and navigator, a dorsal gunner that operated the radio as well, a waist gunner, and a ventral machine gunner. Power was served through 2 x Junkers Jumo 2111F-1 liquid-cooled inline engines of 1,300 horsepower each providing a maximum speed of 273 miles per hour, a range out to 1,430 miles, a service ceiling of 21,330 feet, and a rate-of-climb of 17,000 feet. Defensive armament was 7 x 7.92mm machine guns spread about as two machine guns in the nose section, one in the dorsal position, two machine guns at beam positions, and two machine guns in the ventral position. A 20mm MG FF cannon was fitted either in the nose as well or in a forward ventral gun mounting. Additionally, a 13mm MG 131 machine gun could be fitted in the ventral rear position or at the dorsal position. The typical bomb load maxed at 4,400lbs though up to 7,900lbs could be carried externally - at the cost of speed (increased drag) and the loss of the internal bomb bay (bomb racks restricted use of the bomb bay doors).
As with other classic pre-war German designs, the He 111 served throughout the whole war and over any front the Germans fought at. Its medium bomber role was gradually evolved out of battlefield necessity which showcased the versatility of the excellent design. Germany did not commit heavily to heavy bomber forms for it believed its medium bomber groups and fighter-bomber types were more valuable than lumbering heavies - which the Allies extensively relied on.
He 111s were debuted during the Spanish Civil War (1936-1939) which gave the Luftwaffe the active test ground to further its tactics and prove its new technologies. He 111B-1 aircraft served under the "Condor Legion" banner in the war. It was then used during the Polish "blitzkrieg" campaign which subdued Warsaw and began the rise of the Reich Empire by force. Additional sorties then followed during the lull in direct action, nicknamed the "Phoney War" period lasting from October 1939 to April 1940. Additional service then saw the He 111 back in action during the conquests of Denmark and Norway prior to the French campaign of May 1940.
He 111s were useful medium bombers capable of undertaking various sortie types during its service tenure but it was during the Battle of Britain during the summer of 1940 that its weaknesses were finally brought to light against a determined British fighter and Anti-Aircraft gun defense. He 111s proved too slow to outrun danger and their defensive gun network lacked all-around capabilities which forced the Germans to commit more to escort fighter groups which, in turn, lacked the fuel necessary to engage enemy interceptors for long periods of time. He 111s were, however, still effective bombers and hit British military infrastructure such as radio centers, airfields, and even the English capital (London). As a direct assault platform, however, its days were numbered and the Battle of Britain ended in a stunning German defeat.
Such limitations are what forced the evolution of the line and the story of the He 111 was not written in full by this time in the war. It continued in service as a bomber during the Balkans invasion and was in play as a torpedo bomber platform during the War in the Atlantic against Allied shipping. The aircraft line was then deployed in number across North Africa and the Middle East where it still held value and contributed to the Malta offensive under lightened enemy air defenses.
When Germany committed to the invasion of the Soviet Union in June of 1941 (Operation Barbarossa), all new problems greeted German logistics and the He 111 was pressed over an unforgiving Eastern Front for years. Low-flying ground attacks became the norm as did transport service due primarily to the He 111s inherent operational range. The He 111 was present at the classic Battle of Stalingrad and the Battle of Kursk though losses to Soviet ground-based fire and interceptors proved damaging to German He 111 numbers.
The End of the Line
From early 1943 onwards, the He 111 had seen its best fighting days behind it and Allied air superiority continued to grow while Axis-controlled territories shrank. The He 111 was quickly proving obsolescent and its performance was not getting any better against new generations of Allied aircraft and airmen. The terror campaign was a painful, yet ultimately doomed, initiative by the Germans that pressed He 111s in the rocket delivery role. By now, British response times were excellent thanks to new aircraft and an efficient radar/communications network. Despite their obsolete label, the end of German-operated He 111s came only with the end of the war in May of 1945.
Some He 111s continued into the post-war years with other powers and few survive today (2014) as preserved museum showpieces. The RAF Museum of Hendon has one in their collection as does RAF Duxford. Spanish forms were license-built by CASA as the Model 2.111 and these managed a service tenure into 1975. The Japanese Army evaluated the He 111 as the Army Type 98 but elected against adopting it into inventory.