New Zealand's elite SAS soldiers have received a multi-million dollar fleet of new special operations vehicles, although just how many remains top secret.

The rugged high-tech cross-country Special Operations Vehicles – Mobility Heavy (SOV-MH) have been delivered by British vehicle specialists Supacat and will roll into service over the coming months.

Designed for the world's elite special forces units, the HMT Extenda MK2 can be used either as four- or six-wheel machines depending on the crack soldiers' mission or terrain.

Its "open architecture" means it can be fitted with varying amounts of armour, or none at all, depending on operational needs, Supacat said in a statement.

The off-roaders can be fitted with an "optional mine blast and ballistic protection kit" as well as a range of weapon systems including 12.7mm / 7.62mm machine guns and 40mm automatic grenade launchers, communication equipment and intelligence, surveillance, and target acquisition and reconnaissance (ISTAR).

It's not yet clear the exact final cost of the new fleet. In 2015, the Government approved funding of $28 million to replace the ageing fleet of Pinzgauer Special Operations Vehicles that suffered badly in Afghanistan and prompted then-Defence Minister Gerry Brownlee to say in 2016: "This experience, combined with the demands of contemporary missions and equipment, has led to the need to replace the Pinzgauers with a range of more modern vehicles that keep our elite Special Operations Forces at the leading edge."

For operational security reasons, the number of vehicles in the New Zealand Special Air Service (SAS) Regiment fleet is kept under wraps.

In 2014, Australia awarded a $105m contract to Supacat to deliver 89 Special Operations Vehicles - Commando (SOV-Cdo).

The Defence White Paper 2016 noted that New Zealand's Special Operations Forces need to be trained and equipped to deploy across a range of operations, from long-range reconnaissance to domestic counter-terrorism and explosive ordinance disposal.

The new vehicles, manufactured at Supacat's assembly facilities in Australia, come after the New Zealand Defence Force spent $59 million replacing the Army's guns.

Last year, the MARS-L rifle (Modular Assault Rifle System – Light) replaced the old Steyr 5.56mm guns as part of the upgrade which also included new advanced optical sights, grenade launchers and support and simulation gear.

About 250 NZDF personnel have been serving on 11 operations overseas over the Christmas period, with almost half deployed to Iraq, working alongside the Australian Defence Force as part of a Building Partner Capacity (BPC) mission.