History of the Atlantic Cable & Undersea Communications
from the first submarine cable of 1850 to the worldwide fiber optic network

HMTS Monarch (4) - later CS Sentinel (2)
by Bill Glover

Renamed CS SENTINEL (2)

Built in 1946 by Swan, Hunter & Wigham Richardson Ltd

Length 479.8' Breadth 55.7' Depth 27.8' Gross tonnage 8962

The loss of CS Faraday (2) and CS Monarch (3) left British cable companies without a cable ship capable of cable laying, so the GPO decided to have a new cable ship built. The design was prepared by the Engineer in Chief of the GPO and was completed in 1942. The keel was laid in 1944, the ship was launched on the 8th August 1945 and handed over to the GPO in February 1946.

Cable engine sheaves for Monarch (4) during manufacture
by Garton & King, Exeter Foundry, Exeter, Devon.
Images courtesy of the Garton & King history website.

HMTS Monarch (4) was the largest cable ship afloat at that time, with four cable tanks, each 41 ft in diameter, having a storage capacity of 125,000 cubic feet and providing storage for 2500 nm of deep sea telegraph cable. When laying deep sea coaxial telephone cable and repeaters, 1500 nm of deep sea cable could be carried.

HMTS Monarch moored at Greenwich Loading cable into tanks aboard Monarch

All the cable machinery, which consisted of a double picking up-paying machine forward and a single paying out machine aft, was electrically driven. A trough ran from the repeater storage to the stern, along which the repeaters travelled on a trolley to the stern, where they were launched with a small parachute attached to prevent them from sinking too quickly.

Taking on cable for TAT 1 (1955/56) at
Submarine Cables Ltd. Ocean Works, Erith

The cable machinery and bow and stern sheaves were changed and modified a number of times. The final change was in 1968 when the bow sheaves consisted of three sheaves of which the port one was 6 ft 10 in. in diameter with a flat profile and the other two were the normal 'V' sheaves 6.0 ft in diameter. The stern one was a 7.0 ft diameter 'V' sheave fitted on the port side.

HMTS Monarch (4) after the 1968 refit
Image courtesy of Roger Horton

Educational/promotional poster showing Monarch after the refit

The first task undertaken was the repair and renovation of existing cable networks, which had been neglected during World War II. One example was the repair of the former Direct United States Company cable, between Porthcurno - Newfoundland and Halifax, Nova Scotia which required 1200 nm of new cable to be laid to get it back into working order.

HMTS Monarch laying lightweight
coaxial cable over the stern sheave
Chief Testing Officer in Testing Room
Detail of test equipment

Telegraph Museum Porthcurno has a three-metre model of the ship, and provides a guided tour of it in this video:

On the 1st October 1969 all of the GPO cable fleet lost the prefix HMTS and became CS. This was due to the GPO ceasing to be a Government department. Monarch was sold to Cable & Wireless Ltd., on the 13th October 1970 and was renamed CS Sentinel (2). Based at Bermuda Sentinel was used for cable maintenance in the Atlantic and also for trials of the Scarab submersible. Arrived at Blyth, Northumberland on the 25th October 1977 for scrapping.

Taking on fresh water
Detail of fresh water boat Aquator

Monarch loading HAW-1 at Submarine Cables Ltd., Erith
Detail of cable loading gear

Painting by Jack Pountney
Monarch on the Thames at Greenwich, 1959.
Old Royal Naval College in the background
Image copyright © 2009 Keir Pountney

HMTS Monarch (4) anchored off Sesimbra during
the laying of the 1969 UK-Portugal cable
Image courtesy of Roger Horton


1947 Aldeburgh, England - Domburg, Holland No 6
1950 Weyborne, England - Fano, Denmark
1950 Römo, Denmark - Leeuwarden, Holland
1952-4 Cape Canaveral - Vero Beach - Jupiter Inlet, Florida - Grand Bahama Island (two landings) - Great Stirrup Cay - Great Egg Island - Eleuthera Island (two landings) - Cat Island - San Salvador - Long Island - Acklins Island - Mayaguana Island - North Caicos - Grand Turk.
From Grand Turk two cables ran to Port Daiman, Dominican Republic and from there one cable to Cape La Roca - Grand Estero River - Savana La Mer - Port Macao, all in the Dominican Republic.
Final section was Port Macao - Desecheo Island - Guanajibo Point, Puerto Rico, for the USAF.
1953 Recife, Brazil - St Vincent, Cape Verde Islands
1954 Four power cables across the St Lawrence River from Manicouagan - Petit Metis
1956 TAT-1 Oban, Scotland - Clarenville, Newfoundland - Sydney Mines, Nova Scotia
1957 HAW-1: San Francisco, USA - Hawaii
1958 138kv power cables Vancouver Island - British Columbia mainland
1958 Bournemouth, England - Jersey, Channel Islands
1959 TAT-2 Penmarc'h, France - Clarenville, Newfoundland - Sydney Mines, Nova Scotia
1960 Marske by the Sea, England - Gothenburg, Sweden
1960 USA - Puerto Rico
1961 CANTAT 1 Oban, Scotland - Hampden, Newfoundland; Corner Brook, Newfoundland - Grosses Roches, Quebec
1961 Cape Dyer, Baffin Island - White Bay, Newfoundland
1962 COMPAC Sydney, Australia - Auckland, New Zealand - Suva, Fiji - Hawaii - Port Alberni - Vancouver, British Columbia
1963 Winterton, England - Borkum, Germany (Two cables laid)
1963 Winterton, England - Esbjerg, Denmark
1964 Covehithe, England - Katwijk, Norway
1964 SEACOM I Jessleton (Sabah) - Singapore
1964 SEACOM I Jessleton - Hong Kong
1965 SEACOM II Hong Kong - Guam - Madang, Papua New Guinea - Cairns, Australia
1967 Kristiansand, Norway - Thisted, Denmark
1968 Scarborough, England - Kristiansand, Norway
1968 SAT 1
1969 Sesimbra, Portugal - Goonhilly, England
CS Alert (4) laid the shore ends

CS Sentinel (2) formerly HMTS Monarch (4)

Last revised: 5 March, 2023

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