Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Vessel | Origin | Type | In service | Unit |
| --- | --- | --- | --- | --- |
| Oliver Hazard Perry class | United States | Frigate | 2.0 | Anti-Submarine Unit |
| Kobben class | Norway | Submarine | 4.0 | Submarine Unit |
| Kilo class | Soviet Union | Submarine | 1.0 | Submarine Unit |
| Orkan class | East Germany | Fast Attack Craft | 3.0 | Missile Vessels Unit |
| Tarantul class | Soviet Union | Corvette | 2.0 | Missile Vessels Unit |
| Project 888 | Poland | Training Ship | 1.0 | Support Unit |
| Project 281 | Poland | Rescue Ship | 2.0 | Support Unit |
| Project 5002 | Poland | Rescue Ship | 2.0 | Support Unit |
| Project 863 | Poland | Reconnaissance Vessel | 2.0 | Reconnaissance Group |
Question:
What type of ship is a Kobben class vessel that has been in service longer than 2?
Answer:
Submarine