Submarine Escape Training Tank (SETT), HMS Dolphin

Submarine Escape Training Tank (SETT), HMS Dolphin

The SETT is a vertical escape training tank aligned north-west to south-east, encased in a rectangular tower and surrounded at ground floor by a broadly rectangular arrangement of support accommodation and offices.

CONSTRUCTION AND MATERIALS

Design drawings and photographs show that the building is supported on piles with a concrete base slab. It is of steel-framed construction. The tower has always been clad in corrugated sheet, now replaced with modern re-cladding. The ancillary structures are encased in red brick. The tank itself is made up of welded steel panels.

PLAN AND LAYOUT

The circular escape tank is situated broadly at the centre of the building. The main entrance to the north-west opens onto a spinal corridor. To the north-east of this corridor are an administration office, a group of medical rooms including a sick bay, and a small classroom. To the south-west are offices, WCs and a large classroom. A garage is located to the north-east of the tank, and the staff entrance to the south-west. A lift and stairs providing access to the tower are located to the west and north of the tank respectively. The south-eastern part of the building contains a large plant room with a suit store to its north-west and a laundry in the south-west corner. To the north-east of the plant room is the Submarine Escape Immersion Equipment (SEIE) store.

EXTERIOR

The flat-roofed support building is a utilitarian structure of varying heights in red brick stretcher bond with continuous concrete plat bands forming the headers and cills of its windows. The windows have been replaced with modern uPVC units within the original openings. Concrete is also used in the coping to the parapet. The main entrance elevation faces north-west, where a central bay, slightly set forward, houses the pedestrian door flanked by triple lights.

The rectangular tower rises to ten storeys, broadly central to the support building. It is steel-framed and clad in replacement corrugated sheeting, understood to have been re-clad circa 1995. It has replacement double-glazed windows, also circa 1995, centrally placed in each elevation on floors 2-9. On the north-west and south-east elevations these are triple lights with the flanking lights fixed and the central, larger light an opening hopper. On the other elevations are single-light hoppers. The tenth floor projects such that its elevations stand proud from the line of the main tower. This floor has a flat replacement corrugated sheet roof and a more complex window design of triple lights in each elevation.

INTERIOR AND SUPPORT SPACES

The garage has external access in its north-east elevation as well as pedestrian access to the SETT. Both the SEIE store and laundry have exposed ceilings of concrete beams. The floor in the south corner of the building, which is approximately 30 centimetres thick, hides a water tank below.

TOWER LEVELS AND FACILITIES

The tenth floor contains the top of the circular tank and a decompression chamber. The steel construction is exposed with cross bracing to the walls and a high ceiling of large steel girders. Hoists allow the lifting of equipment in and out of the tank. Floor 9 houses a tank containing air for the decompression chamber above. Floor 7 contains the first air lock at 9 metres depth. Floors 6 and 5 contain offices. Floor 4 houses the 18-metre air lock. Floor 3 contains offices. The students' rest room with WCs and changing facilities is on Floor 2, and similar facilities for staff are on Floor 1. Floor 2 also houses a blister air reservoir allowing instructors to stay at depth rather than having to constantly rise to the surface.

TANK DESIGN

The circular tank is free-standing within the tower, supported by its own weight and that of the warm, chlorinated water it contains. Descending depths are painted on the side of the tank at five-metre intervals. Small circular observation windows are set within the tank wall, along with wall-mounted short ladders and access hatches. At the top of the tank on the tenth floor are steps, hand rails and further ladders allowing access in and out of the water.