Inchindown oil tanks

Inchindown oil tanks are a disused underground fuel depot near Invergordon in Ross-shire, Scotland. Carved into rock during the Second World War for the Royal Navy, they are best known today for their acoustics: they hold the record for the longest reverberation of any man-made structure.

What are the Inchindown tanks?

The site is a group of six enormous tunnel-like tanks hidden inside a hillside above the Cromarty Firth. They were built as a bomb-proof reserve of furnace fuel oil for the Royal Navy base at Invergordon. Sources give different construction dates: some say work ran from 1938 to 1941, while the Highland historic environment record and the listing text give 1938 to 1943.

How big are the tanks?

Five of the six tanks are about 237 metres (778 ft) long and 9 metres (30 ft) wide, with arched roofs 13.5 metres (44 ft) high. The sixth is shorter but has the same height and width. Dimensions vary slightly because the tanks were fitted to the local geology. A single tank holds roughly 5.6 million gallons of fuel, and the whole depot could store around 32 million gallons, or about 100,000 tons.

How did the fuel reach the base?

Pipes about four miles long linked the depot to the naval base at Invergordon. The fuel ran downhill, so three pumping stations were built to send it back up the slope. The largest stands at Tomich.

Why are the tanks famous for their echo?

Long, tall, empty tunnels with hard walls act like a giant reverberation chamber. In 2014 the Inchindown tanks overtook the Hamilton Mausoleum for the longest reverberation on record. The figure given is 112 seconds after a blank round was fired from a pistol, the longest measured in any man-made structure.

Heritage protection

In 2014 the site was listed at Category A, the top tier of Scotland's historic building designations. The tanks no longer store fuel and are not a typical attraction open to every visitor.

Frequently asked questions

Where are the Inchindown tanks? Near Invergordon in Ross-shire, northern Scotland, beside the Cromarty Firth.

What were they used for? As a bomb-proof store of furnace fuel oil for Royal Navy ships based at Invergordon.

How many tanks are there and how large are they? There are six. Five are about 237 m long, 9 m wide and 13.5 m high; the sixth is shorter.

What record do they hold? The longest reverberation in any man-made structure: 112 seconds, measured in 2014, beating the Hamilton Mausoleum.

Can you visit? The site is disused and protected as a Category A listed structure. Check whether organised access is available before planning a trip.