The national flag of Indonesia, which is known as Sang Saka Merah-Putih ("The Sacred Red-and-White") or Bendera Merah-Putih ("The Red-and-White Flag") or simply Merah-Putih ("The Red-and-White"), or sometimes referred to as Sang Dwiwarna ("The Bicolor") in Indonesian is based on the banner of the 13th century Majapahit Empire in East Java. The flag itself was introduced and hoisted in public at the Indonesian Independence Day ceremony, on 17 August 1945.
The design of the flag has remained the same ever since. The design of the flag is simple with two equal horizontal bands, red (top) and white (bottom) with an overall ratio of 2:3. The flag is similar to the flag of Poland and flag of Singapore. The flag is identical to the flag of Hesse (a German state) and flag of Monaco, excluding the ratio. Red represents courage, while white represents purity of intent.
The Naval Jack of Indonesia is reserved for sole use by Indonesian Navy. It flies from every active Indonesian war ship mast. The design of the jack is described as nine alternating stripes of red and white. It is nicknamed Ular-ular Perang (War Pennant or literally "War Snakes"), probably due to the stripes' design. The naval jack dates to the age of Majapahit Empire. The Majapahit Empire, which was renowned for its great maritime strength, used to fly similar jacks on its vessels.source: wikipedia