Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_name_32 ( letter VARCHAR, operator VARCHAR )

### Question ###
Which letter has an operator of the Defense Information Systems Agency?

### Accurate SQL ###

SELECT letter FROM table_name_32 WHERE operator = "defense information systems agency"