This instalment enters the world of superyachts. Robert heads to the English Channel with record-breaking yachtswoman Dame Ellen Macarthur while Ashley travels to the Mediterranean for a ride on a £6million Pershing speedboat.

High-performance planes come under the microscope as Robert takes a look at the private jet of choice for celebrities and royalty, the Cessna Citation X. And Ashley takes a flight with the Blades, the world's only passenger airline that doubles as an aerobatic display team.

The intrepid duo compare two high-tech fire engines. Ashley heads to Glasgow to try out a brand-new aerial rescue platform, and Robert gets to grips with Bristol Airport's Cobra 2 - a bright-yellow fire-fighting machine.

Robert Llewellyn and Ashley Hames test their knowledge of extreme machines. This show focuses on huge warships. Ashley visits an enormous American aircraft carrier in the Pacific and Robert steps aboard the HMS Bulwark, a landing dock in the Baltic Sea.

The star of the show is the all-terrain vehicle. Robert heads to Devon to get to grips with the Jackal - a robust military vehicle; while Ashley is in Wales to test the Eagle 4 hovercraft.

The intrepid duo turn their attention to two mighty rescue rigs. Robert visits the RNLI's most advanced lifeboat, while Ashley hitches a lift with the Scottish coastguard's impressive Sikorsky helicopter.

The intrepid duo turn their attention to supercars. Ashley is dealt the Bowler Nemesis, a rally-winning off-road monster; while Robert is given the Caparo T1, a road-legal racing car.

The duo turn their attention to helicopters. While Robert heads to Cornwall to get to grips with the A109 multi-role chopper, Ashley visits Alabama in the US to experience the fearsome power of the AH-64 Apache.

The duo turn their attention to earthmovers - mechanical monsters designed to excavate and transport huge quantities of dirt. While Robert checks out the Cat D-11 in Spain, Ashley heads to Arizona to hitch a ride in the Liebherr T282.