Measurement posts for sonar and the sailing laboratory HNLMS Paets van Troostwijk
To carry out experiments with underwater acoustics, the Royal Navy used a raft moored alongside the anti-submarine warfare school ship HNLMS Zeearend in the Waalhaven, Rotterdam. The experiments were negatively influenced by navy divers using the same raft.
A simple solution was found. During the occupation of the Netherlands by the Germans, armoured steel doors closed off the German bunkers (pen) for Schnellboote (SBB) in this harbour. The compartmentalised doors (‘pen door’) were made of half-inch steel plates and sized approximately (lwh) 4 x 3 x 2 metres. After lifting, these pen doors could be used as pontoons with enough headroom in the pontoon. A new raft was constructed from two of these pontoons. The raft, with a measurement hut on top, was completed in the autumn of 1948. The raft was stationed in the same Waalhaven and placed under the supervision of the anti-submarine warfare school. This raft enabled the laboratory to carry out underwater acoustic measurements with self-developed transducers.
In addition to this test facility, a second opportunity arose soon. In 1924, a whaler named Thor Junior was built at the Akers Mekaniske Verksted A/S, Oslo, Norway. The ship was renamed Istre. In 1937, the vessel with an accompanying floating tear boiler was acquired by a German company. The ship was renamed again; it became the Süd III. During the war, the Süd III was part of Vorpostenflottille 17 in the Gulf of Finland as ship V1708. The Germans equipped the ship with brass hydrophones (diameter 8 to 9 cm, 12 cm long and a two-core cable at the rear) that were embedded in the ship’s skin for tests with noise detection systems. Ultimately, those hydrophones disappeared behind a layer of paint. In 1946, the ship was handed over to the Netherlands as part of the German WW II reimbursements after which it ended up at a scrapyard. In 1948, a Dutch naval officer was tipped off about this ship that had a large amount of electronics onboard. Upon further investigation, this turned out to be German sonar (‘ASDIC’) equipment. The Royal Navy attempted to acquire the ship for free but was unsuccessful. In the end, an amount had to be deposited.
In early 1949, the ship was completely refurbished by Nederlandse Dok- en Scheepsbouwmaatschappij (NDSM) in Amsterdam for the Royal Netherlands Navy as a sailing test laboratory for ASDIC research and experiments. The damage to the existing equipment was repaired and several improvements were made (including indication and reverberation-controlled gain).
From 1 July 1949 on, its bow code was “HE 1” (Hulpschip Experimenteel 1, which is Dutch for Auxiliary ship Experimental). On 3 May 1950, the ship received its name HNLMS Paets van Troostwijk from Queen Juliana. In the period 1950 – 1951, the ship sailed with the NATO bow code (Auxiliary) A893. In 1950, the first ASDIC tests were carried out in the Nieuwe Waterweg, followed by a trip to Toulon on the Mediterranean. Many experimental trips followed in the next years.
In 1961, it became clear that the old “Paets van Troostwijk” would not be able to fulfil its services as a sailing testing platform anymore for a long time. The Navy formally removed the operational role of the ship on February 13, 1963.
When the ship’s demolition was unavoidable, the Royal Netherlands Navy provided a permanent test rig in Hoek van Holland as an underwater acoustics facility to TNO. This consists of scaffolding with a hoisting mechanism and a shelter for the equipment. This jetty is connected via a fixed walkway to an onshore laboratory. Necessary provisions were made for moving and hoisting heavy loads. TNO has used this facility for experiments with sonar equipment since 1966.