Six members of the bench from the 17-10 win over Samoa come into the side - with Lloyd Burns, Gethin Jenkins, Bradley Davies, Tavis Knoyle, Scott Williams and Leigh Halfpenny promoted into the starting XV.
And they are joined by Stephen Jones, who will make a record 101st appearance for Wales, Ryan Jones, Lee Byrne, Aled Brew and Craig Mitchell.
Only Jonathan Davies, Alun Wyn Jones, Sam Warburton and Toby Faletau retain their places, while Andy Powell remains on the bench.
"On the back of two tough and intensely physical matches we have been able to make some changes to the squad, but also bring a lot of experience into the side at the same time," said Gatland.
"Stephen, Ryan and Gethin in particular bring a wealth of experience but we have some previously established combinations elsewhere in the side as well, in the second row, the midfield and at half-back, so we are excited and looking for this side to do well against Namibia.
"They will be hurting after their loss to South Africa, but we will be concentrating on ourselves and our own performance.
"This is the Rugby World Cup and every performance counts, we showed great heart and courage last week to grind out a win and this week we need to do similar, but also improve and take that next step towards qualification from this incredibly tough group."
Wales: 15 Lee Byrne, 14 Leigh Halfpenny, 13 Jonathan Davies, 12 Scott Williams, 11 Aled Brew, 10 Stephen Jones, 9 Tavis Knoyle, 1 Gethin Jenkins, 2 Lloyd Burns, 3 Craig Mitchell, 4 Bradley Davies, 5 Alun Wyn Jones, 6 Ryan Jones, 7 Sam Warburton (capt), 8 Toby Faletau.Replacements: 16 Ken Owens, 17 Ryan Bevington, 18 Luke Charteris, 19 Andy Powell, 20 Lloyd Williams, 21 Rhys Preistland, 22 George North
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