Thanks Coff .
I was just trying to date the shots as it looked to me that the strakes weren't present.
Historically they were on the Tiger Moth of course, also on the unfortunate Percival Prentice.
Ref. the latter. The Prentice was having awful spin recovery problems with many ( ineffective) solutions being tried.
One day a couple of members of the Prentice design team saw a "Tigger" Moth parked at Luton proudly displaying its strakes .
The lead ( an Irishman) then expounded .
"Be Jesus- that's not a bad idea!"
or so the story goes........