That's not a standard date format I believe. You need to convert it to one
The calculation turns out to be fairly convoluted - you may be able to simplify it:
Don't know - obviously the normal, plus numeric.
Hi Mister X,
Though the Data Type was assigned a date field in Tableau, it is not in a date format that Tableau is able to read as a date. In order for Tableau to recognize it as a date, it needs to be structured as a month day year in the data source (i.e. 2/14/2012 or February 14, 2012). Once the date is in a format in the data source that is recognized by Tableau, then the format can be changed in Tableau to look like 2012 W2.
By using the calculation that Alex provided, it converts the Date field to a date that can be recognized as such by Tableau.
Hope this makes sense!