7 July ,1915

The First Battle of the Isonzo comes to an end.

On June 23, 1915, exactly one month after Italy declared war on Austria-Hungary, the Italian army attacks Austro-Hungarian positions near the Isonzo River, in the eastern section of the Italian front; it will become the first of twelve Battles of the Isonzo fought during World War I.

Of all the fronts of the Great War, the Italian was the least well-suited not only for offensive operations but for any form of warfare at all. Four-fifths of Italy’s 600-kilometer-long border with Austria-Hungary was mountainous, with several peaks rising above 3,000 meters. Despite this, the Italian chief of staff, Luigi Cadorna, desperately wanted to satisfy the demands of his government–as well as the other Allies–by making substantial gains of territory against Austria-Hungary upon Italy’s declaration of war on May 23, 1915.

For its part, Austria-Hungary was surprisingly unconcerned with the Italian entry into the war, despite the fact that it opened a third front for an army whose resources were already stretched dangerously thin. In the years before the war, the Austrian commander in chief, Conrad von Hotzendorff, had often suggested a pre-emptive strike against Italy, as well as against Serbia; in 1915, the prospect of confronting an inferior Italian army seemed to lend a new burst of energy to the Dual Monarchy. Germany, though, pressured Austria-Hungary to fight defensively in Italy and not to divert resources from the Eastern Front against Russia. As a result, while the Italians plotted ambitious offensive operations, including surprise attacks across the Isonzo River, the Austrians settled into their positions in the mountains along the rapid-flowing Isonzo and planned to mount a solid and spirited defense.

After a series of preliminary operations on various sections of the front, Italian forces struck the Austrian positions at the Isonzo for the first time on June 23, 1915, after a one-week bombardment. Despite enjoying numerical superiority, the Italian forces were unable to break the Austro-Hungarian forces, Cadorna having failed to assemble adequate artillery protection to back up his infantry troops–a mistake similar to those made early in the war by commanders on the Western Front. Two Austro-Hungarian infantry divisions soon arrived to aid their comrades at the Isonzo and the Italians were prevented from crossing the river; Cadorna called off the attacks on July 7.

In the four battles fought on the Isonzo in 1915 alone, Italy made no substantial progress and suffered 235,000 casualties, including 54,000 killed. Cadorna’s plans for a highly mobile Italian advance had definitively failed, and battle on the Italian front, as in the west, had settled into slow, excruciating trench warfare.

7 May 1915

A German submarine U-20 sinks the RMS Lusitania, killing 1,198 people.

On May 7, 1915, a German U-boat operating off the coast of Ireland fired a torpedo into RMS Lusitania, causing the massive ocean liner to list precariously and then sink in just 18 minutes. The attack, part of Germany’s campaign of unrestricted submarine warfare, killed 1,198 passengers and crewmembers, including 128 Americans. Contrary to popular belief, this did not directly precipitate U.S. involvement in World War I. Yet it did serve as a widespread propaganda tool and rallying cry once American doughboys began shipping out overseas two years later.

Known as the “Greyhounds of the Seas,” Lusitania and its sister ship, Mauretania, were the fastest passenger liners of their age, capable of crossing the Atlantic Ocean in under five days. At more than 30,000 gross tons each, they were also the world’s largest liners from their launch in 1906 until being surpassed by Olympic and Titanic in 1910 and 1911, respectively. Said to be “more beautiful than Solomon’s Temple and big enough to hold all his wives,” Lusitania attracted a plethora of wealthy, prominent passengers. On its ill-fated final voyage, for example, those onboard included millionaire heir Alfred Vanderbilt, Broadway producer Charles Frohman and actress Rita Jolivet, as well as art collector Hugh Lane, who was purportedly traveling with Rembrandt and Monet paintings stashed away in sealed lead tubes. They were joined by a former British member of Parliament, an amateur boxing champion and a special envoy to the king and queen of Belgium, not to mention businessmen, nurses, would-be soldiers and children. What’s more, as secret documents and evidence gathered at the wreck site would later show, Lusitania had 4.2 million rounds of rifle ammunition, 1,250 cases of shrapnel shells and 18 cases of non-explosive fuses hidden away in its cargo hold, bound for the Western Front.

20 March 1915

Albert Einstein first published his general theory of relativity.

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In 1905, Albert Einstein determined that the laws of physics are the same for all non-accelerating observers, and that the speed of light in a vacuum was independent of the motion of all observers. This was the theory of special relativity. It introduced a new framework for all of physics and proposed new concepts of space and time.

Einstein then spent 10 years trying to include acceleration in the theory and published his theory of general relativity in 1915. In it, he determined that massive objects cause a distortion in space-time, which is felt as gravity.

Albert Einstein, in his theory of special relativity, determined that the laws of physics are the same for all non-accelerating observers, and he showed that the speed of light within a vacuum is the same no matter the speed at which an observer travels. As a result, he found that space and time were interwoven into a single continuum known as space-time. Events that occur at the same time for one observer could occur at different times for another.

As he worked out the equations for his general theory of relativity, Einstein realized that massive objects caused a distortion in space-time. Imagine setting a large body in the center of a trampoline. The body would press down into the fabric, causing it to dimple. A marble rolled around the edge would spiral inward toward the body, pulled in much the same way that the gravity of a planet pulls at rocks in space.