Welsh Cavalry soldiers are reported to be rolling toward the key town of Basra after a successful wave of night-time attacks in southern Iraq.
Scimitar tanks of the Queen's Dragoon Guards - the largely Welsh tank regiment - moved ahead of Royal Marines to secure a beachhead on the coast of the Gulf close to Iran.
They were said on Friday to be spearheading a route north toward Basra, from where troops may push further to Baghdad.
About 2,000 service men and women from Wales are stationed in the region, providing a range of frontline and back-up expertise as part of the US-led coalition to oust the Iraqi regime.
Many troops made a final phone call home ahead of starting operations in the desert.
The Guards are a 318-year-old unit with its roots in a regiment formed by James II and recruited mainly from Wales, Herefordshire and Shropshire.
1st QUEEN'S DRAGOON GUARDS
Has roots in units formed by James II in 1685
Modern regiment formed in January 1959
Comprises troops from Wales, Herefordshire and Shropshire
Queen Mother's funeral, 2002
Their role is normally reconnaissance, and preparation for the next phase of the invasion.
The beach stands on the Al Fao peninsular, which is Saddam's vitally important oil export sea route. Its capture is key to the success of the invasion as a whole.
Soldiers relatives, like the parents of Dragoons Lance Corporal Nicholas Sawicz of Wrexham, are waiting as their loved ones advance.
"It's been nervewracking since December, when he told us he was going. These last few days have really hit home." Dave Sawicz, Nicholas' father, said.
They urged the public to get behind UK troops.
But on Thursday hundreds took part in a wave of protests around Wales against the conflict.
Council workers at two authorities in south east Wales were allowed to take part in a lunchtime demonstration.
In central Cardiff police made five arrests after violence as around 200 protesters blocked the main Kingsway road alongside the castle, causing long delays for drivers.
Fifteen protesters were arrested and released without charge after they chained themselves to the tax office at Carmarthen.
The Muslim community in Wales has expressed its sadness at the start of the military campaign.
The seven bishops of the Church in Wales have called for prayer and reflection in response to the hostilities against Iraq.
On Friday Anglican churches in Neath, south Wales are opening their doors for public prayers for peace and for the armed forces.