Ammo Jetty is the benchmark Perth shore dive, the place where a large share of the city's divers did their first open-water dives and where many still go for night dives. Built in the early 1900s to load munitions from the Woodman Point magazine, the T-shaped timber and concrete jetty runs about 100 m out into Cockburn Sound. The bottom slopes gently from the beach to about 9 m at the head, so the whole dive stays shallow, sheltered and easy to navigate.

The pylons carry the interest. After more than a century in the water they are covered in sponges, ascidians, hydroids, bryozoans, small branching corals and anemones, and each pylon is its own habitat. Macro photographers work them slowly for nudibranchs, flatworms, shrimps, juvenile fish and the occasional seahorse. Crested and red-lipped morwong, old wives, fan-bellied leatherjackets, boxfish, toadfish and bullseyes shelter in the shade under the deck. On the rubble and silty sand you find octopus, cuttlefish, blue swimmer crabs, stars and, at night, crayfish, squid and hunting cephalopods. Dolphins and the odd Australian sea lion have been seen along the jetty.

What Ammo lacks is scenery on a large scale. Visibility averages 3–6 m and the fine silt rises at the first careless fin kick, so good buoyancy and a slow pace pay off. On a good autumn morning after days of easterlies the water can clear to 10–15 m and the jetty is very photogenic.

It suits students, returning divers, photographers and anyone wanting an easy night dive. Experienced divers treat it as a reliable second-choice site when the ocean coast is closed. Parking is simple, there are toilets and a shower on the path, and the gear carry is short.

From Fremantle drive south on Cockburn Road for about 10 km and turn west onto Nyyerbup Circle into John Graham Reserve (Woodman Point). There are two car parks near the main area; most divers use the left-hand lot and kit up there. A signed path on the right side of the car parks leads to the beach in about a three-minute walk with gear.

Walk in from the sand beside the jetty and descend once you reach the first pylons. The usual pattern is to swim out along one side of the jetty and return along the other; Howies recommends going anti-clockwise so the sun is behind you. Allow roughly 40 minutes from the Perth CBD, 20 minutes from Rockingham.

Cockburn Sound shelters the jetty from most ocean swell, so it is often diveable when the northern beaches are not. Aim for swell below about 1.5 m with a period near 11 seconds and light winds, preferably easterly. The summer south-westerly sea breeze (the Fremantle Doctor) usually arrives around midday and chops up the surface and the silt, so dive in the morning or at night.

Strong north-westerlies ahead of winter fronts put waves onto the beach and ruin visibility for a day or two. Heavy rain and plankton blooms in spring can also cut visibility to a metre or less.

Enter beside the jetty's shore end and descend at the first set of pylons in 2–3 m. Follow one row of pylons out to the T-head at about 8–9 m, look through the cross-bracing and the rubble at the end, then cross under the jetty and come back along the opposite side. Keep a metre off the bottom to avoid stirring silt.

Do your safety stop on the pylons coming back in, staying away from anglers' lines at the surface.

Perth's standard training and shore-dive venue: Perth Scuba, Dolphin Scuba, Bucket List Diver and other metro dive schools run Open Water training, guided shore dives and night dives here several times a week, especially when northern sites are blown out.