Among the myriad of sub-plots attached to tomorrow afternoon’s showdown at the Aviva, not the least intriguing is the match-up between Joe Schmidt and Warren Gatland; arguably the best two head coaches in the tournament.

The two Kiwis have played with each other once, against each other once, and coached against each other once, albeit as assistants, so this is their first head-to-head as head coaches, so to speak.

They were team-mates in an invitation match, opponents in a Waikato-Manawatu game as players and a Chiefs-Blues game as assistant coaches. They finally go mano-a-mano after accumulating impressive silverware hauls in recent times, with Schmidt lording trophies in Europe and Gatland at Test level.

Aside from their inside knowledge of each other, Schmidt is quick to point out Gatland has coached nine of Ireland’s starting team, who in turn know his methods.

“Some of them got injured and didn’t have a lot of time on tour, others spent a lot of time on tour with him. They give insights into how he’s thinking and what he’s developing.”

“Then, I suppose, you get that double jeopardy where you start to think ‘Well, he knows we might do this or we might do that’ when we’ve had a half-hour session and a one hour session this week. I don’t think we’re going to do a lot different to what we did this week because you can’t afford to get too complicated.”

Gatland has made little secret of Wales’ intention to be very physical and direct. With that in mind, although the worst of the forecast bad weather is expected to have passed come kick-off, the wet conditions are more liable to favour the bigger team, ie Wales.

After the “relatively simple gameplan” of last week Schmidt acknowledged Ireland will have to be more efficient in their use of the ball, and box cleverer against bigger opponents.

“I think we’d always want to keep our opposition guessing. I guess we’ve just got to do the best job of that we can, not be too blatant in what we’re doing and not be too visible in how we’re setting up a shape to run a play.

“If conditions are tough we’re just going to have to make sure we can mask whatever we are going to play and be really efficient in how we do play it and then resource it really well,” said Schmidt, highlighting the Welsh line speed in defence and the poaching ability of Toby Faletau, Sam Warburton and, off the bench, Justin Tipuric.

“The one thing you try to be is sharper on your feet so that you can get maybe a half an arm or a soft shoulder as opposed to full contact with these guys because you can’t win collisions against a man who weighs 10 kilos more than you do.”

Schmidt’s response to the anticipated Welsh cavalry charge in midfield has been to re-unite Gordon D’Arcy with Brian O’Driscoll, two players who were given their Irish debuts by Gatland.

Schmidt revealed his thinking had always been to restore D’Arc, a view re-enforced by the battering Luke Marshall took in the Scotland game which has prevented him training this week.

There is also D’Arcy’s “familiarity” with O’Driscoll, which may resolve a few defensive issues from last week, as well as giving the kind of directness O’Driscoll had to bring in the second half.

Aside from Leinster and the pair’s record 52 Tests together, the Sexton-D’Arcy-O’Driscoll 10-12-13 axis has started 17 Tests.

The selection for the England game a fortnight hence at “12”, as elsewhere, hinges on tomorrow’s developments. D’Arcy knows the well-established Welsh focus on dominating the midfield channels has raised the ante for him. As for the size differential, it’s nothing he hasn’t usually defied.

“Everybody is the same height around the ankles,” he said, adding: “I’m 90 kilos; I’m not going to try and stop anybody dead. I play my game and I defend my game. I’m a chop-focussed tackler, and I always have been, and it’s been an effective tool for me.

“Once you get somebody around the ankles there is little or nothing they can do. You’ve got to back up that tackle. If they break out of it, then they are on their way but I’m pretty confident in my defence.”

It’s a reprise of his autumn experience, when recalled for the New Zealand game.

Asked if Schmidt’s praise for his display that day pleased him, D’Arcy said dryly: “Not really; we lost. You’ve got to go back to the context of the New Zealand game and what happened. I didn’t play the week before and again when asked about this before, I spoke about Luke and neither one of us is in front or behind; we’re neck-and-neck and each player has to play well when given the chance.

“He played well last week and I have to play well this week and I have to stake my claim and show I have to be there week in and week out.

“I don’t care about Twickenham, I only care about what happens in 48 hours’ time. If I give everything for that game and we win, if I don’t play at Twickenham, obviously I’ll be disappointed. But my immediate concern is half-two on Saturday afternoon.”

He’s not the only one.