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:
| Class | Railway number(s) | Quantity | Year(s) of manufacture | Type |
| --- | --- | --- | --- | --- |
| BW | 1–5 | 5 | 1887–1900 | A1 bm |
| DW ( de ) | 1–5 | 5 | 1895–1901 | A1 n2 |
| DW ( de ) | 6–17 | 12 | 1903–1909 | A1 h2 |
| AW | 1 | (1) | (1897) | Bo′2′ g2t |
| DWss ( de ) | 1 | 1 | 1907 | (1A)2′ h2 |
Question:
What is the class of the a1 bm type?
Answer:
BW