These aircraft distinguishing marks for the aircraft of the principal nations are shown in the accompanying illustration. In order that the aircraft carrying them may be distinguished both from above and below these marks are painted on the upper side of each upper wing and on the lower side of each lower wing of aeroplanes and on both the upper and lower sides of the gas bags of dirigible airships and balloons. The marks are also carried on the sides of the fusilage near the bow and on the sides of the vertical rudders of aeroplanes in many cases. These distinguishing marks are necessary for the aircraft employed in war in order that friend may be distinguished from foe by the airmen and by the gunners and riflemen afloat and ashore. [Illustration: UNITED STATES GREAT BRITAIN] [Illustration: FRANCE BELGIUM] [Illustration: ITALY RUSSIA] [Illustration: GERMANY AND AUSTRIA TURKEY AIRCRAFT DISTINGUISHING MARKS] [Illustration: SEAL OF THE U. S. WAR DEPARTMENT] CHAPTER IV UNIFORMS AND INSIGNIA OF THE UNITED STATES ARMY The uniforms for the officers and enlisted men of the United States Army are made of blue cloth for wear on dress occasions and of olive-drab colored material for wear on general service and field service occasions, and in addition the officers have uniforms of white linen or cotton duck for wear as a dress uniform in the tropics or during hot weather. The service uniforms of the olive-drab color are made of woolen cloth or serge for cold weather and of cotton duck for hot weather, the latter being usually known as “khaki” uniforms, though the regulation color is of a somewhat darker shade than that universally known as “khaki.” [Illustration: _Copyright by Underwood & Underwood_ General Tasker H. Bliss, Chief of Staff, U. S. Army, and Major General Hugh L. Scott, U. S. Army] It is a general rule that the officers serving with the troops in garrison or in the field must appear in the same style of uniform as that prescribed for the enlisted men. During peace times officers serving on detached duty or in the offices of the Departments where there are no enlisted men on duty ordinarily wear civilian clothes, but in time of war all officers and enlisted men are required to wear the olive-drab service uniform at all times except when the full dress and dress uniforms are prescribed for some appropriate special occasion. Officers ordered on active field service are required to carry with them only the service uniforms. UNITED STATES ARMY OFFICERS’ UNIFORMS Commissioned officers of the Army are required to have complete outfits of service uniform (woolen olive-drab for temperate and cold weather and cotton olive-drab or “khaki” for the tropics and hot weather), dress uniform, full dress uniform, white uniform and special evening dress uniform, and for wear on certain occasions in the evening a mess dress uniform of blue and one of white is optional.