Officially designated as fleet service ships, the three  vessels of the Type 423 Oste class are purpose built SIGINT/ELINT and reconnaissance ships of the German  Navy. They replaced the Type 422 class.
Accommodation for the crew was designed to civil standards, and the Oste  class offers much more comfort for the crew than other ships in the  German Navy.
Ships of the class
 A 50 Alster
A 52 Oste
A 53 Oker
The ships were built at Flensburger  Schiffbau-Gesellschaft in Flensburg.
All ships are currently based in Eckernförde  and belong to the 1st submarine squadron stationed in Eckernförde. The  vessels got the same name and pennant numbers as the three Type 422  class vessels they replaced. To avoid the confusion, the ship names are  sometimes suffixed with II.
The Oker is an intelligence ship of the German  Navy. She is the lead ship of the German Navy's Type 423.
The Oker is meant as a reconnaissance ship, with a wide  array of modern elektromagnetic, hydroacoustic and electro-optic sensors  for strategic intelligence gathering. She can be used as an advanced  warning unit. The design was originally intended to gather data on  Soviet ships.
The Oker is seen here departing Faslane