Coastal Forces of the Royal New Zealand Navy Coastal Forces was a division of the Royal Navy established during World War II . It consisted of small coastal defence craft such as motor launches , submarine chaser s , air - sea rescue launches , motor gun boats and motor torpedo boats . It did not include minesweeper s , naval trawler s or landing craft . This article is about the equivalent boats used in the Royal New Zealand Navy ( RNZN ) . From 1921 until 1941 the New Zealand Navy was a Division of the Royal Navy . The RNZN was not created until 1 October 1941 . Within six months of its creation the RNZN commissioned twelve Class B Fairmiles and sixteen Harbour Defence Motor Launch es ( HDMLs ) RNZN Fairmiles . On 4 April 1941 the British War Cabinet approved a proposal for a striking force of anti - submarine motor - boats , six at Auckland , four at Wellington , and two at Lyttelton . Drawings and specifications of the Fairmile anti - submarine motorboat developed by Fairmile Marine were sent from England and it was agreed that these craft could be built in New Zealand providing the engines , ordnance and some prefabricated components came from England . The Class B Fairmiles were long , displaced 85 tons and had a complement of 16 . Twin 12 - cylinder petrol engines generated on each of two shafts for a speed of . They were armed with a 2 pdr gun , a 20 mm Oerlikon cannon , twin 0 . 303 in machine guns and 12 depth charge s , and were fitted with ASDIC ( sonar ) . The orders were distributed among four Auckland firms . The estimated cost of each vessel was £35 , 000 , making a total of £420 , 000 for the twelve . Delays occurred in the delivery of prefabricated components , the difficulty in getting supplies of first - class kauri timber and a serious shortage of skilled labour . The newly formed RNZN commissioned the 12 Class B Fairmiles on 20 December 1943 and assigned pendant number s Q 400 through to Q 411 . The boats were not initially named , and were identified only through their pendant numbers . The first Fairmile constructed , " Q 403 " , was launched on 29 September 1942 and commissioned on 21 October 1942 . Thereafter the completed boats were delivered at short intervals . All the boats were completed and were then recommissioned into the newly formed RNZN on 20 December 1943 . RNZN Fairmiles in the Solomons . On 14 January 1944 , Admiral Halsey , Commander South Pacific , informed the New Zealand Naval Board that the " current employment of Japanese submarines and estimates of their future employment indicate immunity from the submarine menace in New Zealand waters " . He proposed that the New Zealand Fairmile motor launches should be employed in the Solomon Islands , relieving American destroyers and patrol vessels for duty elsewhere . The twelve Fairmiles were refitted for service in tropical waters and formed into the 80th and 81st Motor Launch Flotillas . The 80th Flotilla consisted of MLs 401 to 406 and the 81st Flotilla of MLs 407 to 411 . The flotillas were based at Renard Sound in the Russell Islands . The base was named " Kahu " and for administrative purposes ML400 was commissioned on 1 April 1944 as HMNZS " Kahu " . During the seventeen months of their service in the Solomons , from March 1944 until June 1945 , the twelve Fairmiles logged on anti - submarine screen patrols and on escorting ships . They had no encounters with Japanese forces . RNZN Fairmiles post war . All the fairmiles returned to Auckland in July 1945 . In 1946 - 47 all but " Q 411 " were sold to private buyers who used them for passenger and / or cargo service or as pleasure craft . " Q 411 " was sold in 1965 . " Q 409 " was repurchased by the navy in 1953 and resold in 1963 to become the Auckland - Waiheke ferry " Iris Moana " . Two other former fairmiles were renamed the " Ngaroma " and the " Colville " and used as the main ferries between Auckland and Great Barrier Island . They were skippered by Len Sowerby and his son Lester . RNZN Harbour Defence Launches . Sixteen Harbour Defence Motor Launch es ( HDMLs ) purchased in the United States were commissioned between March 1943 and March 1944 . The launches were long , displaced 54 tons and had a complement of 10 . Twin Diesels generated on each of two shafts for a speed of . They were armed with one 20mm Oerlikons , three Vickers K machine guns and six depth charge s . They operated as the 124th and 125th Motor Launch Flotillas , based on Auckland and Wellington respectively . They maintained anti - submarine patrols inside indicator loops . Though they were not tested by enemy action , the anti - submarine fixed defences at Wellington and Auckland attained a high degree of efficiency . After the war , twelve were retained , three were sold and one was transferred to the Army . The remaining boats were refitted and re - engined with Foden diesels . These were subsequently used as fishery protection , survey and reserve training boats . All remaining boats were named and given new pendant numbers in 1950 .