It <i>was</i> an F-4 cannon deal with the grunt phones.  When the M1 was designed the phone was seen as superfluous, so it wasn&#x27;t added.  The Army thought it was obsolete.<p>I&#x27;m actually surprised the Marines didn&#x27;t fit the phones as soon as they transitioned to the M1.  I&#x27;m guessing they didn&#x27;t have budget, since they were getting post-Cold-War Army hand-me-downs.