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_52908 ( "Ship" text, "Date Commissioned" real, "Gross Tonnage" real, "Propulsion" text, "Material" text )

### Question ###
Tell me the sum of Gross Tonnage for isis ship on date commisioned less than 1842

### Accurate SQL ###

SELECT SUM("Gross Tonnage") FROM table_52908 WHERE "Ship" = 'isis' AND "Date Commissioned" < '1842'