Help with formula MID, TRIM

I have a similar question to my previous one.

if i have a list:

WNI J950 Darlston WTT Washout

WI J942 Rigby SEE Washby

list goes on ...

 
i just want to capture the 4 digits J950 or J942 in my other column for each row. For all rows i want the 4 characters only. The problem I’m having if i do mid function it will only work with if i have same number of letters before the 4 characters i need. In this case every row has different amount of letters before and for some rows im only getting 3 characters of the 4 characters i require.

Is there a formula which i can use that will solve this ?

Any help is appreciated