It sounds a bit politically incorrect eighty years later, but you have to admit they have a point: Their tubes are so good that both sides are using them.

In this ad from the July 1938 issue of Radio Retailing, Raytheon proudly announces that they’re selling tubes to both sides in the Spanish Civil War:

When you replace a tube in a radio set, the fate of thousands of lives does not hand in the balance.  The set doesn’t have to operate perfectly, instantly, and over a long period of time!  But if your time is worth money, and your customer’s satisfaction is important, your Jobber can supply you with the identical tubes that both armies in Spain have found to be the most dependable!  And they cost no more!