Editing Karel Doorman-class frigate (section)

== Modernisation ==
The Royal Netherlands Navy and the Belgian Naval Component decided to upgrade the four frigates by rebuilding both hangar and helicopter deck for the NH90 NFH helicopter as well to replace the forward mast for fitting the new Thales SeaWatcher 100 phased array surface search radar and Gatekeeper electro-optical surveillance system. In addition, they were also equipped with a new Low Frequency Active and Passive Sonar (LFAPS).<ref>{{Cite web |url= https://magazines.defensie.nl/materieelgezien/2017/01/mg201701m-fregatten |title=M-fregatten opgeknapt |author=Jack Oosthoek |date=1 February 2017 |website= Materieelgezien |publisher= Defensie.nl |language=Dutch}}</ref> The first ship to receive the upgrade was ''Van Speijk'' in April 2012, next was ''Leopold I'', followed by ''Van Amstel'' and ''Louise Marie'' is undergoing the modernization. SMART-S 3D search radars will not be replaced by SMART-S MK2.

Seawatcher 100 is a non-rotating active phased array radar for naval surface surveillance. The system automatically detects and tracks asymmetric threats and very small objects such as swimmers and periscopes in all weather conditions. Seastar can also be used for helicopter guidance. Seastar is internationally marketed as Sea Watcher 100

Gatekeeper is a 360-degree panoramic electro-optical surveillance and alerter system based on IR/TV technology. Designed to counter emerging asymmetric threats down to small boats and swimmers, Gatekeeper increases short-range situational awareness in littoral environments.

In 2018 the Portuguese Navy decided to modernize its two ''Karel Doorman''-class frigates (Mid-life update), the first frigate started modernization in 2018 and was delivered in September 2021,<ref>{{Cite tweet|title=A fragata NRP Bartolomeu Dias (F333) da 🇵🇹 @defesa_pt @MarinhaPT chega na próxima segunda-feira à Base Naval de Lisboa (BNL) após um período de modernização de meia vida realizado na 🇳🇱.|url=https://twitter.com/defence360/status/1451604715943481352 |author=Defence360° |user=Defence360 |number=1451604715943481352 |language=pt |trans-title=The frigate NRP Bartolomeu Dias (F333) from 🇵🇹 @defesa_pt @MarinhaPT arrives next Monday at Base Naval de Lisboa (BNL) after a half-life modernization period carried out at 🇳🇱.|date=22 October 2021 |access-date=2021-10-25}}</ref> the second frigate started modernization in 2020 and was received in October 2022.<ref>{{Cite web|url=http://www.jornaldaeconomiadomar.com/bartolomeu-modernizada-na-holanda/|title=Fragata Bartolomeu Dias será modernizada na Holanda|language=pt |trans-title=Frigate Bartolomeu Dias will be modernized in the Netherlands |date=2018-04-27|website=Jornal da Economia do Mar|access-date=2019-10-25}}</ref> In November 2024 it was reported that the Portuguese Navy had acquired eight Harpoon Block II conversion kits from the Netherlands.<ref name="AR18112024">{{cite web |url= https://armyrecognition.com/news/navy-news/2024/portugal-modernizes-naval-arsenal-with-harpoon-block-ii-missile-kits |title= Portugal Modernizes Naval Arsenal with Harpoon Block II Missile Kits.|author= <!--Not stated-->|date=18 November 2024|website= Army Recognition}}</ref> These kits can be used to convert Harpoon Block I missiles to Block II, which the Portuguese Navy can launch from its modernized ''Karel Doorman''-class frigates.<ref name="AR18112024" />