Possible Clues:

• Friend caught by a motorway radar, for one
• Tessa, say, intimate before lunch
• NATO, for example
• The longest one in English is the Navy term 'ADCOMSUBORDCOMPHIBSPAC'
• American buddy introduced Ernie, for one
• Short term for mate in America
• eg Ernie; radar
• Only letters from a friend during the morning
• RADA, for example, is a friend to millions
• American ringing friend in UNICEF, perhaps