The Russo-Japanese War of 1904-1905 was the first of the 20th Century wars to rely on modern armaments. This included developments on land and at sea and resulted in a Japanese Empire victory over neighboring Russia. Weapons and doctrine utilized during that conflict did much to influence the direction of an even greater war to follow - World War 1 (1914-1918).
Some observers suggested the new, impending war in Europe to become a fast clash of empires - Austria-Hungary would punish the Serbs for their role in the assassination of its heir. However, before the end of 1914, all of the major European players had committed to the war and all sides bogged down into what became "Trench Warfare". With this derailment of plans, came weapons developed specifically to remove, or neutralize, dug-in enemy force and one development that was refined from designs prior became the infantry hand grenade.
The infantry hand grenade was not a new arrival of period, having been around for some time prior but, by the 18th Century, it had become an all but forgotten weapon in the West. The Russo-Japanese War brought its usefulness back to the forefront as the stagnate nature of Trench Warfare required its services. France, Britain and Germany all revisited the weapon type and planned for its field use accordingly.
This led to the powers of World War 1 using all manner of grenade type weapons in the conflict - egg-, disk- and stick-shaped grenades were all in play. Several other unique forms emerged in the lead up to World War 1 for Germany including the "Kugelhandgranate 1913". The Kugel Grenade showcased a basic spherical shape though the body sported raised sections for maximum fragmentation. Through its top was an igniter that was inserted when the grenade was needed - otherwise a transportation plug was fitted here during travel. The igniter was made of bronze and tube-shaped and carried black powder for the ignition process. The action was triggered by the pulling of a brass wire by the operator which scraped along a friction block. There was a red-coated igniter offering a 5-second fuse and a base ignitor design giving a longer 7-second fuse. As its designation suggests, the Kugel Grenade was introduced in 1913 and available in some number by the time of World War 1 in mid-late 1914. The grenade was designed to explode into dozens of metal fragments, causing maximum carnage at close range and continuous (rather random) damage within a radius beyond. Overall weight was 1 kilogram.
In the early phases of the war, these grenades acquitted themselves quite well. They were inherently lightweight and more reliable than other types, giving good results under harsh battlefield conditions. However, they still remained hand-thrown weapons and its reachable range was only as far as it could be thrown - around 50 feet or less in most cases. Their tactical value could be increased some by using a launcher-type system but this arrangement was not readily available. Various igniter types were fitted over the course of the grenade's service career - all with 5-second delays - and newer variants emerged between 1913 and 1917.
The major development in the line arrived in 1915. By this point, German industry was firmly entrenched in wartime production and its resources pushed to the brink. As such, a more refined, budget-conscious version of the Kugel Grenade was developed as the Model 1915. It was more or less a cleaned up version of the Model 1913 to bring about greater available numbers for the war effort. The fragmentation grooves along the spherical body were redesigned and simplified for mass production but the grenade itself - in both form and function - largely stayed faithful to the original design.
Over time, the value of the Kugel Grenade dwindled to the point that newer, more modern grenades succeeded it - especially the Model 1915 Stielhandgranate which was a German standard for World War 2 (1939-1945) as well. The Kugel Grenade was, however, still available in considerable numbers eso this ensured it remained in the German inventory for the duration of World War 1. Some examples were used in further tests that led to little.