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:
|  | Country | Builder | Location | Ship | Class / type |
| --- | --- | --- | --- | --- | --- |
| 6 March | United States | John Roach and Son | Chester, Pennsylvania | City of Rio de Janeiro | Passenger ship |
| 13 May | Germany | Kaiserliche Werft Wilhelmshaven | Wilhelmshaven | Bayern | Sachsen-class ironclad |
| 13 June | United Kingdom | Royal Dockyard | Devonport, Devon | Pegasus | Doterel-class sloop |
| 31 August | United Kingdom | Royal Dockyard | Sheerness | Gannet | Doterel-class sloop |
| 23 October | Norway | Karljohansverns Verft | Horten | Nor | Vale-class gunboat |
| 1 November | Norway | Karljohansverns Verft | Horten | Brage | Vale-class gunboat |
| 9 November | Germany | A. G. Vulcan | Stettin | Württemberg | Sachsen-class ironclad |
Question:
count how many different classes of ships were launched.
Answer:
4