Machin Mystery

A friend of mine gave me this item. I can’t call it a cover because it didn’t pass through the mail. It is an empty envelope with a Machin on it, and of course it piqued my interest. The Machin is tied to the cover with a hand-stamped “BP.” Other hand stamps are “18577” and “8,” which matches the number after the name.

The back of the item provides a little more information and more mystery. Handwritten on one edge is “North Sea Oil Country / Helio Copter Strike.” In a different handwriting is “Dundas Racing Pigeon Assn 18-5-77,” and above that is the stamped image of a pigeon.

That confirms that the “18577” on the front is a date, and the reference to North Sea Oil would indicate that “BP” is British Petroleum. I also searched and found that “helio copter” is apparently an old term for helicopter.

But what is the “Helio Copter Strike”? Is it a strike in the sense of finding oil, or is it a workers’ strike? What has either type of strike to do with racing pigeons? And what might have happened on 18 May 1977?

Please put any ideas in the comments.

--Larry