 Italian gun positions were located using sound ranging by the British 6th Survey Regiment , Royal Artillery . These positions disclosed themselves by firing at Australian patrols , which now went out nightly , mapping the antitank ditch and the barbed wire obstacles . Aerial photographs of the positions were taken by Westland Lysander aircraft of No. 208 Squadron RAF , escorted by Gloster Gladiator biplane fighters of No. 3 Squadron RAAF . British Intelligence estimated the strength of the Italian garrison at 20 to 23 @,@ 000 with 100 guns , and discounted reports of six medium and seventy light tanks as exaggerated — a serious intelligence failure . 
