Wings Halfpenny (ankle) and Williams (knee) join props Adam Jones (elbow) and Jenkins (calf) in travelling with the squad, although they are at differing stages of recovery from their injuries.
Gavin Henson is also heading for the training camp having
recently been filming
a reality television show.
World Cup is ultimate honour - Roberts
Peel's club, Sale, have blocked the scrum-half from joining Wales summer training, amid an on-going dispute with the Welsh Rugby Union about availabilty outside designated International Rugby Board time periods.
However, his new clubmate Andy Powell is with Wales as his contract with the Aviva Premiership side begins after the
Wales have also announced an open training day at the Millennium Stadium for Tuesday, 2 August.
Gatland said: "It's is a way of letting a few people in to see us who wouldn't otherwise be able to and reaching out to the nation to get behind the side."
WALES SQUAD FOR POLAND TRAINING CAMP
Scott Andrews, Gethin Jenkins, John Yapp (Cardiff Blues), Lloyd Burns (Newport Gwent Dragons), Adam Jones, Paul James, Ryan Bevington, Craig Mitchell, Huw Bennett (Ospreys), Ken Owens, Matthew Rees (Scarlets, capt), Bradley Davies, Sam Warburton, Martyn Williams (Blues), Luke Charteris, Toby Faletau, Dan Lydiate (Dragons), Alun Wyn Jones, Ryan Jones, Jonathan Thomas, Justin Tipuric (Ospreys), Rob McCusker, Lou Reed, Josh Turnbull, (Scarlets), Andy Powell (Sale).
Leigh Halfpenny, Richie Rees, Jamie Roberts Lloyd Williams, (Blues). Aled Brew, Jason Tovey (Dragons), Andrew Bishop, Shane Williams (Ospreys), Jonathan Davies, Tavis Knoyle, George North, Rhys Priestland, Scott Williams (Scarlets), Lee Byrne (Clermont Auvergne), Michael Phillips (Bayonne), James Hook (Perpignan), Gavin Henson (unattached).
WALES PRELIMINARY RUGBY WORLD CUP SQUAD
Huw Bennett (Ospreys), Lloyd Burns (Dragons), Richard Hibbard (Ospreys), Matthew Rees (Scarlets), Ken Owens (Scarlets); Scott Andrews (Cardiff Blues), Ryan Bevington (Ospreys), Paul James (Ospreys), Gethin Jenkins (Cardiff Blues), Adam Jones (Ospreys), Craig Mitchell (Exeter Chiefs), John Yapp (Cardiff Blues); Luke Charteris (Dragons), Bradley Davies (Blues), Alun Wyn Jones (Ospreys), Lou Reed (Scarlets); Gareth Delve (Melbourne Rebels), Toby Faletau (Dragons), Ryan Jones (Ospreys), Dan Lydiate (Dragons), Rob McCusker (Scarlets), Andy Powell (Sale Sharks), Jonathan Thomas (Ospreys), Justin Tipuric (Ospreys), Josh Turnbull (Scarlets), Sam Warburton (Blues), Martyn Williams (Blues)
Tavis Knoyle (Scarlets), Dwayne Peel (Sale Sharks), Mike Phillips (Blues) Lloyd Williams (Blues), Richie Rees (Blues); Stephen Jones (Scarlets), Rhys Priestland (Scarlets), Jason Tovey (Dragons), James Hook (Perpigan); Andrew Bishop (Ospreys), Jonathan Davies (Scarlets), Gavin Henson (Unattached), Jamie Roberts (Blues); George North (Scarlets), Aled Brew (Dragons), Morgan Stoddart (Scarlets), Scott Williams (Scarlets), Shane Williams (Ospreys); Lee Byrne (Clermont Auvergne), Leigh Halfpenny (Blues).
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