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_203_193 ( id number, "ship name" text, "in service" number, "project number" text, "type" text, "class" text, "comments" text )

### Question ###
what is the difference in years between the first ship put into service and the last ?

### Accurate SQL ###

SELECT MAX("in service") - MIN("in service") FROM table_203_193