Personnel are putting in flood barriers to protect an electrical substation that powers more than 9,000 homes in Doncaster.
Two hundred British soldiers from the UK Standby Battalion, based at Catterick in North Yorkshire, have deployed to the flood-hit area of South Yorkshire.
Personnel from the Light Dragoons and 2 Royal Anglian are also trying to bolster flood defences to train lines which connect Leeds to Doncaster.
Trooper Sam McIvor, 2 Troop, C Squadron, Light Dragoons, said if the area saw more rain it risks flooding the train lines and more homes:
"If the rain comes in the river will rise in height, the water will come over the tracks and cause a lot of problems - trains won't be able to go.
"There's also a possibility the housing estate will start getting flooded," Tpr McIvor added.
Lieutenant Elliot Black, 1 Troop Leader, C Squadron, Light Dragoons, said they're following advice from the Environment Agency and Network Rail.
"We're just providing the manpower and the boot strength to make sure the tasks get done quickly and in an effective manner," Lt Black said.
A further 200 servicemen and women are also being put on immediate readiness.
The Prime Minister announced more support will be provided for communities hit by flooding, after a meeting of the Government's emergency COBRA committee.
Personnel from the Light Dragoons and 2 Royal Anglian began relief work in Stainforth, Doncaster, on Wednesday morning.
As well as laying down sandbags and shoring up the village's bridge, personnel will also support potential evacuation efforts and keep residents informed.
Boris Johnson has faced criticism from political rivals, who accused him of dragging his feet in response to the floods.
Labour leader Jeremy Corbyn, who visited the Bentley Town End area of Doncaster on Tuesday, said that Number 10's response had been "woeful", while Liberal Democrats leader Jo Swinson said the issue was not being taken seriously enough.
Mr Johnson visited Stainforth on Wednesday morning, where he was accused of having "not helped" following the flooding.
Severe flooding hit parts of Yorkshire and the East Midlands last week, including areas around the River Don near Doncaster.
In the last few days, an RAF Chinook was sent to the Doncaster area to bolster flood defences after British Army Royal Engineers saw the need for military helicopter support.
Launched from 18 Squadron, RAF Odiham, crew from the Joint Helicopter Support squadron at RAF Benson transported ballast to flood banks through to the early hours of the morning.
Thirty-five flood warnings are still in place across England, with people in affected areas being urged to heed warnings of emergency services.
Boris Johnson has announced relief funding will be made available for those affected by the floods. There will be £500 per eligible household.
Speaking after the COBRA meeting, Mr Johnson said the country must "prepare for more floods" this winter, urging communities to listen to the advice of emergency services.