When the Luftwaffe was publicly unveiled, the He 51 was its poster aircraft. Neat, modern-looking and pleasant to fly, it featured in displays and propaganda as evidence that Germany was once again a serious air power. For a year or two the image held — before combat exposed how quickly the state of the art had moved on.

There was a hard logic to the display flights and photo opportunities. A visible, credible fighter arm was a diplomatic instrument as much as a military one, meant to impress rivals and reassure the public. For that purpose the He 51 was ideal: it looked purposeful, flew well in a demonstration, and existed in numbers when much of the rest of the rearmament programme was still on the drawing board.

Equipping the wing that bore the Red Baron’s name gave the He 51 an outsized symbolic role. It was the aircraft on which many of the Luftwaffe’s earliest fighter pilots learned their trade, forming the nucleus of squadrons that would soon convert to the Bf 109.

In that sense the He 51 was a bridge aircraft. The pilots, ground crews and squadron structures built up around it did not disappear when the type was retired — they carried straight over to the monoplanes, taking with them the habits and discipline learned on the biplane.

Against the Republicans’ early, mixed fleet the He 51 did well enough. But the balance of the air war shifted the moment modern Soviet fighters appeared. What had looked like a capable front-line fighter at home was revealed as a machine already overtaken by events.

Spain was the first time the reborn Luftwaffe tested its equipment in real combat rather than on the exercise field, and the He 51 took that test. The verdict it returned — that biplane fighters were finished and that speed now trumped agility — was uncomfortable, but it arrived early enough to act on.

Spanish and Soviet pilots nicknamed their Polikarpovs the Chato (“snub-nose”, the I-15) and Mosca (“fly”, the I-16). The monoplane I-16 in particular could choose the terms of every fight. For He 51 pilots it was a brutal lesson in what a faster, more modern aircraft could impose on an older one.

The experience left a deep mark on German fighter thinking. Pilots who came home from Spain were convinced that speed, climb and the freedom to choose when to fight mattered more than tight turning — a conviction that shaped how they later flew the Bf 109, favouring fast, energy-based slashing attacks over swirling close-in dogfights.

Rather than throw the type away, the Germans put it to work at low level, attacking troops and positions. The work was hazardous but valuable, and it helped the Luftwaffe develop the close-support methods it would use to devastating effect in the opening campaigns of the Second World War.

Ground attack in a slow biplane was punishing work. Pilots ran the gauntlet of rifle fire and light flak at low altitude, with little armour and less speed to protect them. That the He 51 kept doing useful damage says as much about the courage of its pilots as about the aircraft — a reminder that an obsolete design can still be dangerous in determined hands.

Galland, who would later command Germany’s fighter arm, cut his combat teeth flying low-level attack missions in the He 51. It was unglamorous, dangerous flying — a long way from the high-altitude duels he became known for — but it was formative experience for one of the war’s most influential airmen.

Galland was not alone. A whole cohort of future Luftwaffe leaders rotated through Spain, and the He 51 was often the aircraft on which they first heard shots fired in anger. The combat experience they gained gave the German fighter arm a cadre of battle-tested commanders that few other air forces could match in 1939.

The Bf 109’s speed, climb and firepower made the contrast with the He 51 stark and immediate. The monoplane revolution was no longer a theory to be argued in staff colleges; it was flying overhead in Spain, and the He 51 was on the wrong side of it.

For the He 51 the arrival of the Bf 109 was both a rescue and a retirement notice. It relieved the biplane of a job it could no longer do, and made explicit what Spain had already implied: the He 51’s front-line career was over.

Spanish crews continued to operate the He 51 in the ground-attack and training roles, flying the type into the early 1940s. For Spain it remained a useful workhorse long after Germany had relegated it to secondary duties.

This hand-me-down pattern was typical of the era: front-line aircraft that had lost their edge were passed to allies and second-line units rather than scrapped. In Spanish service the He 51 soldiered on in the attack and training roles into the early 1940s, outlasting its German front-line career by several years.

The He 51 was never a major export success — by the time it was available for sale it was already dated — but Bulgaria took a small number, operating them as fighters and trainers. Export figures for the type are modest and not always precisely recorded.

The He 51’s limited export record is itself telling. By the time it was available abroad it was neither cutting-edge nor especially cheap relative to newer designs. Its small overseas footprint is another quiet measure of how narrow its window of relevance really was.

The He 51W swapped the wheeled undercarriage for twin floats, exploring the idea of a shipboard or coastal fighter. It never entered widespread service, but it is a reminder of how many roles designers tried to squeeze from a single interwar airframe.

Float-fighter experiments were common in the 1930s, when navies were still working out how to project air power without a full carrier fleet. The He 51W was Germany’s modest contribution to that line of thought. It went nowhere — floats cost too much speed for too little gain — but it shows how open the design questions of the period still were.

Docile, forgiving and available in numbers, the He 51 made a serviceable advanced trainer. Thousands of hours were flown teaching cadets the fundamentals of a powerful single-seater before they graduated to the aircraft that would actually fight the war.

It is easy to overlook the training role, but it may be where the He 51 did its most lasting work. Every hour a cadet spent mastering a powerful single-seater on a forgiving biplane made him safer and more effective on a Bf 109. In that unglamorous job the He 51 quietly contributed to the Luftwaffe’s early-war strength.

Judged as a combat aircraft the He 51 was a disappointment. Judged as the machine that re-established German fighter production, trained the first Luftwaffe fighter pilots and delivered the unambiguous message that the biplane era was over, it did an important job. Sometimes the most useful aircraft are the ones that teach you what you can no longer get away with.

That is why the He 51 deserves to be remembered honestly rather than dismissed. It was obsolescent almost on arrival, beaten in its only serious air war, and left no roll of famous victories. Yet it rebuilt an institution, blooded a generation of pilots and delivered a clear verdict on the direction of air combat — all in a few years.