| 1964-feb | Ordered | Ordered  A133 HMS Hecla | |
| 1964-feb | Ordered | Ordered A137 HMS Hecate | |
| 1964-feb | Ordered | Ordered A144 HMS Hydra | |
| 1964-may-06 | Laid down | Laid down A133 HMS Hecla Yard No 2256 | |
| 1964-may-14 | Laid down | Laid down A144 HMS Hydra Yard No 2258 | |
| 1964-oct-26 | Laid down | Laid down A137 HMS Hecate Yard No 2257 | |
| 1964-dec-21 | Launched | Launched A133 HMS Hecla | |
| 1965-feb | Aircraft | Aircraft A137 HMS Hecate Assigned 829 Sq Wasp HAS.1 XT432 as Hecate Flt/418-HT, until c Mar 1967 | |
| 1965-mar-31 | Launched | Launched A137 HMS Hecate | |
| 1965-jun-09 | Commissioned | Commissioned A133 HMS Hecla | |
| 1965-jul-14 | Launched | Launched A144 HMS Hydra | |
| 1965-oct-20 | Commissioned | Commissioned A137 HMS Hecate | |
| 1966-may-05 | Commissioned | Commissioned A144 HMS Hydra | |
| 1966-aug-27 | Deployment | Deployment A137 HMS Hecate present at Plymouth Navy Days 1966 | |
| 1966-aug-27 | Deployment | Deployment A133 HMS Hecla present at Plymouth Navy Days 1966 | |
| 1967-aug-26 | Deployment | Deployment A133 HMS Hecla present at Plymouth Navy Days 1967 | |
| 1968-jun | Aircraft | Aircraft A137 HMS Hecate Assigned 829 Sq Wasp HAS.1 XS532 as Hecate Flt/418-HT, until c Nov 1969 | |
| 1969-jul-26 | Deployment | Deployment A137 HMS Hecate Fleet Review: Ships of the Western Fleet Present at Ships of the Western Fleet review in Torbay, flying the flag of the Hydrographer of the Navy. | |
| 1969-nov-07 | Ordered | Ordered  A324 SAS Protea | |
| 1970-jul-20 | Laid down | Laid down A324 SAS Protea | |
| 1970-aug-29 | Port Visit | Port Visit A137 HMS Hecate Ship open to visitors at Plymouth Navy Days 1970. | |
| 1970-nov-19 | Deployment | Deployment A144 HMS Hydra Operation Burlap to Bay of Bengal to assist in cyclone relief efforts | |
| 1971-jul-14 | Launched | Launched A324 SAS Protea | |
| 1971-sep | Aircraft | Aircraft A144 HMS Hydra assigned 829 NAS Wasp HAS.1 XT436 as Hydra Flt/419, until c Jun 1977. | |
| 1971-sep | Aircraft | Aircraft A137 HMS Hecate Assigned 829 Sq Wasp HAS.1 XS562 as Hecate Flt/418-HT, until c Feb 1973 | |
| 1972-may-23 | Commissioned | Commissioned A324 SAS Protea | |
| 1972-oct | Refit | Refit A144 HMS Hydra refit at Singapore, late Oct 1972 until mid Feb 1973 | |
| 1972-nov-09 | Laid down | Laid down A138 HMS Herald | |
| 1973-oct-04 | Launched | Launched A138 HMS Herald | |
| 1974-oct-12 | Port Visit | Port Visit A144 HMS Hydra visited Suva during Oct 1974 | |
| 1974-oct-31 | | A138 HMS Herald Ship No 512 built at Leith shipyards of Henry Robb (Robb Caledon) for more info see www.leithshipyards.com | |
| 1974-nov-22 | Commissioned | Commissioned A138 HMS Herald | |
| 1977-apr-17 | Port Visit | Port Visit A137 HMS Hecate visited Monaco as Flagship of Hydrographer of the Navy, for 11th International Hydrographic Conference, 18-30 Apr | |
| 1977-jun-25 | Deployment | Deployment A138 HMS Herald Fleet Review: Silver Jubilee of HM The Queen Present at Silver Jubilee Fleet Review, off Spitsand | |
| 1977-jun-25 | Deployment | Deployment A133 HMS Hecla Fleet Review: Silver Jubilee of HM The Queen Present at Silver Jubilee Fleet Review, off Spitsand | |
| 1977-jun-25 | Deployment | Deployment A137 HMS Hecate Fleet Review: Silver Jubilee of HM The Queen Present at Silver Jubilee Fleet Review, off Spitsand | |
| 1978-sep | Deployment | Deployment A144 HMS Hydra Departed Portsmouth for 1st 6 month winter section of a 3 year survey contract in Iran, in co-operation with HMS Herald. Contract cut short by Iranian Revolution of Mar 1979 | |
| 1979-jul | Aircraft | Aircraft A138 HMS Herald assigned 829 NAS Wasp HAS.1 XT794 as 010 Flt / 325 until Apr 1984 | |
| 1981-sep | Deployment | Deployment A144 HMS Hydra departed UK for 6 month survey mission in Caribbean. 829 NAS Wasp HAS.1 XS568 / 415 embarked. | |
| 1981-oct | Deployment | Deployment A138 HMS Herald departed UK for 7 month survey mission to Middle East waters | |
| 1981-nov-24 | Deployment | Deployment A324 SAS Protea Operation Kerslig Stood off Luanda, as support vessel for clandestine operation to damage the Petrangol refinery. | |
| 1982-mar-02 | Deployment | Deployment A133 HMS Hecla Departed HMNB Devonport on a 5 month North Atlantic deployment, due back Aug 1982. | |
| 1982-apr | Aircraft | Aircraft A144 HMS Hydra assigned 829 NAS Wasp HAS.1 XT432 as Hydra Flt/415, until c Sep 1982. | |
| 1982-apr-14 | Deployment | Deployment A133 HMS Hecla Operation Corporate Ordered to South Atlantic departing Gibraltar on 20 Apr for CASEVAC operations, leaving theatre on 29 Jun 1982. | |
| 1982-apr-15 | Refit | Refit A138 HMS Herald medical facilities enhanced at Portsmouth, for maritime ambulance role in South Atlantic. Completed 23 Apr. | |
| 1982-apr-16 | Aircraft | Aircraft A133 HMS Hecla 829 Sq 012 Hecla Flt (/416 allocated but not carried) formed, with Wasp HAS.1 XT420 which was sent to Gibraltar via RAF Hercules and embarked 20 Apr. | |
| 1982-apr-24 | Deployment | Deployment A138 HMS Herald Operation Corporate Departed HMNB Portsmouth to South Atlantic for CASEVAC operations, leaving theatre 30 Jun 1982 | |
| 1982-apr-24 | Deployment | Deployment A144 HMS Hydra Operation Corporate Departed HMNB Portsmouth to South Atlantic for CASEVAC operations, leaving theatre 27 Aug and returning to Portsmouth on 24 Sep 1982. | |
| 1982-jun | Refit | Refit A137 HMS Hecate single 20 mm Repaint o/a Pussers Grey and fitted with 2x 20mm guns, in preparation for South Atlantic deployment | |
| 1982-jul-23 | Deployment | Deployment A137 HMS Hecate Departed UK for South Atlantic with 829 NAS 013 Flt Wasp HAS.1 XV626 / 414 embarked, to cover as Ice Patrol Ship while HMS Endurance was refitting in UK. Returned to UK via Pacific and Panama Canal, on 18 Feb 1983. | |
| 1985-oct | Refit | Refit A137 HMS Hecate at HMD Devonport until Mar 1986 | |
| 1986 | Decommissioned | Decommissioned A144 HMS Hydra | |
| 1986-jan-17 | Deployment | Deployment A144 HMS Hydra Operation Balsac diverted to Aden for Operation Balsac | |
| 1986-apr | Commissioned | Commissioned  932 KRI Dewa Kembar | |
| 1987 | Refit | Refit A138 HMS Herald 1987-1988 Flight deck strengthening for Lynx operations | |
| 1990 | Decommissioned | Decommissioned A137 HMS Hecate | |
| 1990-aug | Deployment | Deployment A138 HMS Herald departed HMNB Devonport for eastern Mediterranean as support vessel for 2nd MCM Squadron, as build up for Operation Desert Storm began. Later moved into the Gulf around Bahrein. | |
| 1994-jan-29 | Fate: scrapped | Fate: scrapped A137 HMS Hecate to Pipavav, India for breaking up | |
| 1997 | Decommissioned | Decommissioned A133 HMS Hecla to be replaced by HMS Scott | |
| 1998 | | A138 HMS Herald Penant number changed to H138 | |
| 2001 | Decommissioned | Decommissioned A138 HMS Herald | |
| 2001-jul | Fate: transfered | Fate: transfered A138 HMS Herald sold to an Irish Survey company and renamed Somerville | |
| 2004-jun-18 | Fate: scrapped | Fate: scrapped A138 HMS Herald Scrapping began at Alang. | |
Aircraft