Take the M275 into Portsmouth (signed Portsmouth West). From the end of the M275 follow signs for Historic Waterfront/Seafront. This takes you to across three roundabouts to traffic lights by Unicorn Gate (entrance to Naval Base). Continue across these traffic lights, following signs to Gunwharf Quays Shopping Centre. At next set of lights (by HMS Nelson Officers Mess) slight left towards Gunwharf Quays. At next set of lights, turn right into Park Road. At next set, turn left into Burnaby Road. The entrance to the USPHC grounds is 200m on the right.
You may be able to park along Burnaby Road (local parking fees apply), but are advised to park in Ravelin car park (as it is only £2 all day), which is next to the University of Portsmouth Library. To find Ravelin car park, continue down Burnaby Road then turn right - the Library will be straight ahead - drive past the library and turn left into the car park through black metal gates.