"The sound of snail instrument is on Father has to go to guard the sea and sky of Hoang Sa archipelago” This lullaby of a woman in Ly Son, retelling the moment of sending her husband off to the Hoang Sa archipelago in the past, is still existed after hundreds of years. The sound of the special instrument in the lullaby, which is made from the local U snail, still creates the same sad feeling for anyone who hears it. Hundreds of years ago, the U snail instrument was the only means of communication at sea for the Hoang Sa guard team, when they came to the Hoang Sa and Truong Sa archipelagos under the king's order, to plant the first markers to claim the sovereignty rights on those islands./.