Please read the following table in HTML format from a webpage and then answer the question in detail according to the table. Each table cell is defined by a <td> and a </td> tag. Each table row starts with a <tr> and ends with a </tr> tag. 'rowspan=m' and 'colspan=n' represents a cell spaning over 'm' rows and 'n' columns.

Webpage title:
German submarine U-60 (1939)
Table title:
Summary of raiding History
Table:
<table id='hittask' contenteditable='False'>
<tr> <th colspan=1 rowspan=1 > Date </th><th colspan=1 rowspan=1 > Ship </th><th colspan=1 rowspan=1 > Nationality </th><th colspan=1 rowspan=1 > Tonnage (GRT) </th><th colspan=1 rowspan=1 > Fate </th></tr>
<tr> <td colspan=1 rowspan=1 > 19 December 1939 </td><td class="highlighted"  colspan=1 rowspan=1 > City of Kobe </td><td colspan=1 rowspan=1 > United Kingdom </td><td class="highlighted"  colspan=1 rowspan=1 > 4,373 </td><td class="highlighted"  colspan=1 rowspan=1 > Sunk (Mine) </td></tr>
<tr> <td colspan=1 rowspan=1 > 13 August 1940 </td><td class="highlighted"  colspan=1 rowspan=1 > Nils Gorthon </td><td colspan=1 rowspan=1 > Sweden </td><td class="highlighted"  colspan=1 rowspan=1 > 1,787 </td><td class="highlighted"  colspan=1 rowspan=1 > Sunk </td></tr>
<tr> <td colspan=1 rowspan=1 > 31 August 1940 </td><td class="highlighted"  colspan=1 rowspan=1 > Volendam </td><td colspan=1 rowspan=1 > Netherlands </td><td class="highlighted"  colspan=1 rowspan=1 > 15,434 </td><td class="highlighted"  colspan=1 rowspan=1 > Damaged </td></tr>
<tr> <td colspan=1 rowspan=1 > 3 September 1940 </td><td class="highlighted"  colspan=1 rowspan=1 > Ulva </td><td colspan=1 rowspan=1 > United Kingdom </td><td class="highlighted"  colspan=1 rowspan=1 > 1,401 </td><td class="highlighted"  colspan=1 rowspan=1 > Sunk </td></tr>
</table>
Question:
How destructive is U-60?
Answer:
U-60 sank three ships for a total of 7,561 GRT and damaged another one of 15,434 GRT.