David put pen to paper on Thursday morning after completing a medical - and says he is not joining just to make up the numbers.
"There is no point coming just to play in the reserves," he insists. "I'm looking to make the first team, though obviously I am a great admirer of David James, who I regard as the number one for England in the World Cup.
"I have always looked up to him, and hopefully I can learn from him."
The deal came about via a former Hammer recommending him to Glenn Roeder, and David explains: "Kenny Brown jnr is the manager at Barry Town and put me in touch, and I trained with West Ham for two weeks at the start of the year.
"I have thoroughly enjoyed it and Ludo has been great to work with."
David turned down Harry Redknapp's Portsmouth to sign for West Ham, and had no hesitation in making the step up from Wales to the Premiership.
"Glenn Roeder told me that he brought Kevin Phillips from Baldock Town to Watford, so the gap is not impossible," he says.
"And, at 21, I'm only a baby as far as keepers are concerned.
"I have played every game since joining Barry Town from Galway in Ireland this summer, and I opted for West Ham above Portsmouth and other clubs that wanted me."
The fee is £75,000, and David has signed a 2 1/2 year deal.