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_31151 ( "Name/ designation" text, "Year of intro" real, "Country of origin" text, "Primary cartridge" text, "Major users" text )

### Question ###
How many years of introduction does the Neal Submachine Gun have?

### Accurate SQL ###

SELECT COUNT("Year of intro") FROM table_31151 WHERE "Name/ designation" = 'Neal submachine gun'