Wales play Australia in their final Pool A game on Saturday with top spot in the group up for grabs.
“We always planned to make the quarter-finals," Gatland told reporters.
"We knew how tough this group was going to be, not with just England, Australia and ourselves, but Fiji, too. I think if Fiji had been in other groups they would have qualified for the quarter-finals as well."
Gatland pulled no punches in his assessment of the group.
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“It’s not just the group of death, it’s the group of hell," he said.
"So to have qualified now gives us the opportunity to take the shackles off a bit and to start focusing on winning the group.
“We are delighted to be through and Australia have done us a massive favour. You’ve got to feel for other teams involved. There is a huge amount at stake, with families and livelihoods, so I am just trying to keep things in perspective.”
Gatland had sympathy for England coach Stuart Lancaster after his team failed to qualify for the last eight.
“Everyone is talking about England as the first host country to miss out on the quarter-finals but the stupid thing is why was the World Cup draw done three years ago? It’s ridiculous. If they had followed the football model then we wouldn’t be in this position."
Gatland paid tribute to Lancaster's work.
“I have a huge amount of respect for what he has done since he took over in terms of the discipline and the way the players conduct themselves," he said.
"As a coach you learn from adversity and if he gets an opportunity to continue he will learn from this and it’s a massive moment for him as a coach.”
Wales will be able to play with more freedom against Australia at Twickenham on Saturday.
“It gives us the opportunity to go out there and we haven’t got the burden of having to win the game to qualify," Gatland said.
"We followed a pretty rigid game-plan against Fiji but the times we did move the ball we looked dangerous."
“The big thing for us is that we didn’t pick up too many injuries against Fiji but the boys are still sore today. It’s a nice position to be in but if you win this group your road is a little bit easier in the next rounds.”
(Editing by Justin Palmer)
