Black Watch, Barbican, London<br />The Diver, Soho, London<br />The Merry Wives of Windsor, Globe, London

The National Theatre of Scotland's hit paints a shattering portrait of army life in 'the triangle of death'

The scarlet baize of the pub's pool table has started to writhe and bulge, as if something is trying to get out. The blade of a dagger slices through, followed by an arm in military camouflage, like some mythic warrior's birth. A moment later, a squaddie is clambering out and lolling on the side, taking a breather. The table is instantly an armoured vehicle, under a baking sun.

Black Watch is the National Theatre of Scotland's powerful portrait of the renowned Highland regiment which was controversially deployed in Iraq's "triangle of death" in 2004. While still out there, facing suicide bombers and mortar attacks, its soldiers learned that the Government had decided perfunctorily to wind up their close-knit and proudly historic unit.

John Tiffany's epic traverse staging – edged by high scaffolding towers – was first acclaimed at the 2006 Edinburgh Fringe and it remains painfully trenchant, presented now as part of the Bite festival. It combines imaginative theatrical flair with an authentically salty script.

The latter is based on playwright Gregory Burke's interviews with Iraq war veterans whom he first met kicking around in a pub in Fife. Working the interview situation into the drama is a clever stroke too, exposing the edginess of that arts-meets-army encounter – including hair-raising aggression from one mentally scarred soldier who suspects the writer-researcher (played by a nerdy Michael Nardone) of exploitation.

Burke has a sharp eye for brutalised behaviour yet also creates a sympathetic tribute to these brave and long-suffering lads. The action leaps between the pub and vivid memories of the desert, and Tiffany's all-male troupe excels at swaggering and turning the air blue. They capture the sweltering boredom of Camp Dogwood, the joshing macho humour, explosions of internecine rage and the terror of sudden enemy attacks.

The stylised choreography involves a few unconvincing moments. Tiffany has a tiresome liking for expressionistic semaphore. However, the fights (co-ordinated by Steven Hoggett) are impressively fierce, with high lifts, spinning bodies and thrashing legs.

Alluding to the Edinburgh Tattoo, this is a cross between a regimental drill and a ceilidh, sporadically scattering into sprinting, panic-stricken chaos. Electrifying.

The Diver is an intriguing cross-cultural collaboration between Soho Theatre and Toyko's enterprising Setagaya Public Theatre. Overlaying a contemporary crime thriller and several ancient Noh dramas, this chamber piece stars the elfin Kathryn Hunter and the esteemed Japanese devisor-director Hideki Noda.

He plays a forensic psychiatrist, anxiously trying to establish if Hunter's Yamanaka is responsible for murdering a corporate businessman's two children in an arson attack. Mentally deranged or cunningly theatrical, she flits between multiple personalities, insisting she is the folkloric ghost-mother of a lost illegitimate princeling and various legendary mistresses of emperors and their offspring.

Written by Noda and Colin Teevan, The Diver's first exchanges are stiff and the closing Freudian twist is rushed. The staging needs more technical polish too. Several lengths of bright silk are not sufficiently hidden from view before they unravel into floating kimonos and rivers of blood in Yamanaka's fantasies. However, in the main, the intricately interlaced stories are enthrallingly fluid, with slow-spinning sofas and sliding doors, with hauntingly sensual mask work, and gilded fans playfully serving as everything from champagne flutes to slices of pizza.

Harry Gostelow's adulterous prosecutor morphs into Genji, an amusingly smarmy royal bastard, and Hunter is unnervingly mercurial, quivering with terror one minute and the next swanning around with a coquettish smile playing on her lips.

Lastly, Shakespeare's farce The Merry Wives of Windsor proves disappointing at the Globe. Certainly, there's fun to be had as Serena Evans' perky, giggling Mistress Page and Sarah Woodward's dryly humorous Mistress Ford lead the wannabe womaniser, Christopher Benjamin's Falstaff, up the garden path. This literally extends into a long walkway, complete with humpback bridges, winding through the pit's standing crowds.

Yet director Christopher Luscombe is not at his most inspired. Lovely Elizabethan velvet gowns fail to conceal several dull performances. Benjamin as the Fat Knight remains gloriously rotund but, after a warm spry start, his comic energy dwindles.

"Black Watch" (0845 120 7550) to 26 July; "The Diver" (0870 429 6883) to 19 July; "The Merry Wives of Windsor" (020-7401 9919) to 5 Oct