Image copyright Getty Images Image caption The crowd of 50,000 was described as a "sea of khaki" due to the number of military men - many injured - in attendance

The 1915 FA Cup final was notable for the "sea of khaki" created by thousands of soldiers in the stands. It was also the last cup final for four years, as a public debate raged over whether the game should have gone ahead at all during wartime.

While Sheffield United were beating Chelsea 3-0 on an April afternoon, the Second Battle of Ypres was under way on the Western Front where the Germans had unleashed a new weapon - chlorine gas.

Within months many of the crowd, and the players, would be in the trenches Dr Alexander Jackson, National Football Museum

Many were angry that the match was being played and felt football was distracting young men from signing up to fight.

Two days before the game, some 200 people had attended a protest meeting at Manchester's Albert Hall, with one speaker claiming professional football was "the greatest hindrance to recruiting in the United Kingdom".

"Anti-football feeling in many sections of the press had reached its peak before the game," said Dr Alexander Jackson, collections officer at the National Football Museum, in Manchester.

"Newspapers made reference to some criticism, but also a great deal of correspondence from troops at the front saying they wanted football to continue - it gave them something to look forward to during breaks from the fighting."

Image copyright Getty Images Image caption Match reports described fog and rain before the match kicked-off at Old Trafford

Although the game became known as the Khaki Cup Final, due to the presence of so many wounded and on-leave soldiers, the Manchester Guardian reported that a large proportion of the crowd were "young men of military age and not conspicuously unfit for service".

Following the game, the 17th Earl of Derby presented the trophy and told the 50,000 fans that anyone not yet in uniform should now play "a sterner game for England".

"There was probably less of the jubilation and happiness that normally accompanies an FA Cup final tie," added Dr Jackson.

"Within months many of the crowd, and the players, would be in the trenches."

John Garrett, Sheffield United FC historian, said the few photos in existence of the match showed a "very grey atmosphere".

Image caption It marked the end of the professional game for more than four years

"It was raining, very foggy," he said. "Witnesses say that before the game kicked-off at 3.30pm the fog was struggling to lift to a point where you couldn't see the players warming up on the pitch.

"The whole tapestry of the grey, the khaki, the drizzle, the uncertainty, the unhappiness, really paints a bleak picture."

The match was played at Manchester United's stadium as the regular FA Cup final venue of Crystal Palace had been requisitioned for military training.

Travel restrictions were in place, so an alternative venue in the capital was seen as impractical.

Image caption Sheffield United still have the match ball from the 24 April 1915 fixture

Sheffield United were the favourites and had already won the FA Cup three times. Chelsea, founded 10 years earlier, were a club still very much in its infancy and were yet to win any major silverware.

James Simmons put the Blades ahead close to half-time, with late goals from Stanley Fazackerley and Joseph Kitchen sealing the win for the Yorkshire side.

But despite the win, there was none of the normal celebrations.

No victory parade was held and the players were told not to smile in the FA Cup winners' photo. Sheffield United also held no celebratory dinner for five years.

"Bringing the cup back, United were told that they had to return under the cover of darkness," said Mr Garrett.

"The club came back on the train at about midnight. We believe police were employed to move along anyone who was brave enough to turn out to cheer the triumphant Blades coming home."

The Football Association suspended the Football League and the FA Cup later that summer and football only continued on an amateur basis.

The professional game did not return until 1919.