1915 AD., Luxembourg, Marie-Adelaïde, Brussels mint, 10 Centimes, KM 28.

Luxembourg, Marie-Adelaïde, Brussels mint, 1915 AD.,
10 Centimes (ø 20 mm / 3,00 g), zinc, 3,1 (?) g. theor. mint weight, mintage 1.400.000 , axis coin alignment ↑↓ (180°), plain edge, 4,2 mm center hole,
Obv.: GRAND DUCHÉ DE LUXEMBOURG / ·1915· , issuer and date within dotted circles around center hole, .
Rev.: 10 CES , value center hole, two oak branches below.
L. 273-1 ; Weiller 263 ; KM 28 : Schön 7 .

Year / Mintage
1915 / 1.400.000

The German occupation of Luxembourg in World War I was the first of two military occupations of the Grand Duchy of Luxembourg by Germany in the 20th century. From August 1914 until the end of World War I on 11 November 1918, Luxembourg was under full occupation by the German Empire. The German government justified the occupation by citing the need to support their armies in neighbouring France, although many Luxembourgers, contemporary and present, have interpreted German actions otherwise.
During this period, Luxembourg was allowed to retain its own government and political system, but all proceedings were overshadowed by the German army's presence. Despite the overbearing distraction of the occupation, the Luxembourgish people attempted to lead their lives as normally as possible. The political parties attempted to focus on other matters, such as the economy, education, and constitutional reform.

More on https://en.wikipedia.org/wiki/German_occupation_of_Luxembourg_during_World_War_I