Not so weierd... Develop in secret. Once you have it your enemies knows in any case. And if you can maintain plausible deniability it is much easier to keep developing / much less public scrutiny, especially if you already are operating a highly unpopular apartheid state.

I remember that during the war with Cuba in Angola the South Africans deployed their nuke on the border, the Cubans knew this and as such the South African border was never threatend.