The American Cipher Bureau was just another government agency doing then what the NSA does today.

Note that the page describes the Bureau as spying on negotiating partners: "Its most notable known success was during the Washington Naval Conference during which it aided American negotiators considerably by providing them with the decrypted traffic of many of the Conference delegations, most notably the Japanese."

Sound familiar? I see no reason to think that they weren't doing everything else that today's NSA has been caught doing.