Goalkeeper Kyle Letheren and defender Reghan Tumilty joined earlier in the window along with midfielder Mouhamed Niang as Hartley looks to strengthen his squad ahead of the new campaign which begins at Walsall at the end of July.
And the new Pools boss has promised fans there will be more signings to come over the coming days and weeks after insisting there remains plenty of work going on behind the scenes, particularly from head of recruitment Chris Trotter.
“We’ve been so busy, and putting in so many hours. Myself and Gordon and the rest of the staff,” said Hartley.
“Chris Trotter has been brilliant. He’s been doing so much work behind the scenes, he’s a really important person for me. So I’m loving it so far, [but] we want to get to the real stuff.
“I can promise to the Hartlepool fans that there’s a lot more to come,” Hartley added.
“There’s more signings coming in. We want to make the team stronger and to be able to compete in the league.”
Pools, The Mail understands, are keen on Leeds United midfielder Stuart McKinstry with a potential loan deal being lined up to bring the teenager to the Suit Direct Stadium.
And Hartley is hoping the arrival of new players will allow supporters to buy into their approach this season and pack out the Suit Direct Stadium on a regular basis with the Pools boss making a plea to fans to snap up their season tickets ahead of the first home game of the season against AFC Wimbledon on August 6.
“Hopefully we can get more season tickets sold,” he said.
“I think we’re at a good number just now, but hopefully we can have a big push and we can get more season tickets throughout the next few days and coming weeks and for that first home game of the season.
“We want to have a big number here.”