Simmons, who coached Zimbabwe in 2004-05, said the strength in depth in Ireland, who are current Under-19 and Under-17 European champions, convinced him to take the job.
In 2009, Gatland's second Six Nations in charge, he made numerous changes in a bid to improve the side's strength in depth.
They left out former skipper Sanath Jayasuriya after his superb 157 in the first match but had more than enough strength in depth to cope with a Dutch side, who also have their sights set on next year's World Cup in the Caribbean.
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Chelsea are magnificent defensively, and have such strength in depth, work hard and are so resilient.
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However, 25-year-old Graham is confident his side have the strength in depth to cope with their losses.
"Strength in depth is important to build on the success of this year, " said Ospreys manager Derwyn Jones.
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"I have been referring recently to the growing strength in depth of the Scotland squad, " said the head coach.
But while Wales do not have strength in depth at the back, England do boast an embarrassment of defensive riches.
Scarlets wing Mark Jones and Harlequins centre James are big losses, but Welsh rugby has strength in depth in the backs.
The strength in depth on the men's tour today means you cannot afford to let opponents dictate and boss you around the court.
Wasps will also be dark horses but they can't suffer too many injuries because they haven't got a lot of strength in depth.
Only time will tell, but they've got the strength in depth, the experience and the winning habit, so they'll be there or thereabouts.
But Gatland does have more strength in depth at centre with experienced pair Andrew Bishop and Tom Shanklin joined by young Scarlet Jonathan Davies.
Wales have another season to try to add to that strength in depth before the 2011 World Cup and there were encouraging signs in Cardiff.
What they need to do is get on with it and show their strength in depth, but this week is a massive test for them.
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The hallmark of a good team is strength in depth, and England certainly have a number of players in a number of positions pushing for selection.
Gatland believes that open-side flanker is one of the positions that Wales lack strength in depth and Williams' u-turn is a huge boost to the national side.
The former Leicester, Brive and Sharks number 10 says the big difference between Worcester and their play-off rivals is the strength in depth, funded by owner Cecil Duckworth.
South Africa league leaders Ajax Cape Town demonstrated strength in depth to overwhelm Mount Cameroon 5-1 at home despite resting several key players ahead of the four-round championship run-in.
"The potential of the squad is amazing and our strength in depth is one of the best you're going to see in European club rugby, " Williams told BBC Sport.
Brandy offers strength in depth up-front for Swansea as the 19-year-old Old Trafford rookie faces competition from Gorka Pintado, Andrea Orlandi, Guillem Bauza and last season's top-scorer Jason Scotland.
Regional rugby remains controversial, with many areas of the country feeling isolated from the professional game, and others believing that four teams do not offer the necessary strength in depth.
And, despite having 10 players away with Ireland's World Cup squad, they had enough strength in depth to topple the Ospreys and earn a quarter-final away to Irish rivals Ulster.
They arguably lack the strength in depth required for the Tour and the sprinters needed to lead in Robbie McEwen, who defends his green jersey for the team in 2003.
"This tour has given me the type of problems any coach wants - strength in depth with competitive players who all have ambition - and players with quality too, " Jenkins added.
But with Thatcher available, plus the form of Roberts and Crewe youngster David Vaughan - who plays left midfield or left wing-back at Gresty Road - Wales suddenly have strength in depth.
It did not mean those in the team were going to be replaced, but it meant the squad was freshened up, you increased competition for places and you increased strength in depth.
What the defeat proved - other than that errors get ruthlessly punished - was that South Africa have incredible strength in depth, but Wales are now not out of their depth when facing the Tri-Nations sides.
Russia's strength in depth - with six players in the WTA top 20 - proved decisive, with the champions able to retain the trophy in the absence of star names such as Maria Sharapova and Olympic champion Elena Dementieva.
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