|Length:||9.8 miles (15.8 km)|
|Meets:||Unclassified, B4319, A4139|
|Old route now:||A4139, A4075|
|Route outline (key)|
The B4320 is a rural B-road in southwestern Pembrokeshire.
It starts in the centre of the village of Angle, at the T-junction at the east end of the main street, and heads west through the village (although Pembroke is signposted along the unclassified road south). At the other end of the main street it TOTSOs left; this road is unsignposted and appears more minor country lane than B-road.
The road climbs away from the coast, including a very tight hairpin at one point, before finally heading east, with the chimneys of the Milford Haven refinery in the distance. It reaches the direct route south of Angle and then the B4319 a mile later. The road continues in a vaguely easterly direction passing no places of any size for another couple of miles - but it does widen to S2 soon after leaving the national park.
On the southern edge of the village of Hundleton the B4320 TOTSOs left. The route ahead, although unclassified, is signposted as the route to Pembroke. The B4320 continues through Hundleton and detours around a creek before reaching the Pembroke suburb of Monkton. It ends at a T-junction on the A4139 on the bank of the Pembroke River under the walls of the castle.
The B4320 has changed at both ends. Its original western end was by the sea at West Angle Bay. It then headed east through Angle (explaining the TOTSO at the western end of the village) and along the side of Angle Bay, along a route that is now a dirt track. It joined its current route near Hardings Hill.
At the other end, the B4320 continued past Pembroke Castle and along Main Street before heading out of town to the northeast and ending on the A477 to the west of Milton. This section was upgraded to Class I status in the late 1920s. Main Street is now the A4139 and the road to Milton is the A4075.