A pencil bomb was a type of time bomb

Time bomb

A time bomb is a bomb whose detonation is triggered by a timer. The use time bombs has been for various purposes ranging from insurance fraud to warfare to assassination; however, the most common use has been for politically-motivated terrorism.-Construction:The explosive charge is the main...

 with a timer

Timer

A timer is a specialized type of clock. A timer can be used to control the sequence of an event or process. Whereas a stopwatch counts upwards from zero for measuring elapsed time, a timer counts down from a specified time interval, like an hourglass.Timers can be mechanical, electromechanical,...

 that could be set to detonate any given time. It was designed by German chemist, Dr. Scheele and used by German spy Franz von Rintelen

Franz von Rintelen

Captain Franz Dagobert Johannes von Rintelen was a German Naval Intelligence officer in the United States during World War I....

 during World War I

World War I

World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

.

Design

When the bomb prototype

Prototype

A prototype is an early sample or model built to test a concept or process or to act as a thing to be replicated or learned from.The word prototype derives from the Greek πρωτότυπον , "primitive form", neutral of πρωτότυπος , "original, primitive", from πρῶτος , "first" and τύπος ,...

 was first shown to Rintelen by Scheele it was a hollow cylinder of lead the size of a large cigar. Into the middle of the tube a circular disc of copper had been pressed and soldered, dividing it into two chambers. One of these chambers was filled with picric acid

Picric acid

Picric acid is the chemical compound formally called 2,4,6-trinitrophenol . This yellow crystalline solid is one of the most acidic phenols. Like other highly nitrated compounds such as TNT, picric acid is an explosive...

, the other with sulphuric acid or some other inflammable liquid. A strong plug made of wax with a simple lead cap made both ends airtight. The copper disc could be as thick or as thin as desired. If it were thick, the two acids on either side took a long time to eat their way through. If it were thin, the mingling of the two acids would occur within a few days. By regulating the thickness of the disc it was possible to determine the time when the acids should come together. This formed a safe and efficient time-fuse

Fuse (explosives)

In an explosive, pyrotechnic device or military munition, a fuse is the part of the device that initiates function. In common usage, the word fuse is used indiscriminately...

. When the two acids mingled at the appointed time, a silent but intense flame, from twenty to thirty centimetres long, shot out from both ends of the tube, and while it was still burning the lead casing melted away without a trace.

Use

Von Rintelen and his ring of German agents would slip the bombs onto ships carrying munitions bound for the war. The incendiary device ignited cargoes when ships were far at sea. It was estimated later that he alone had destroyed $10 million (US$ million in ) worth of cargo on 36 ships.

Manufacture

The first batch of bombs was manufactured on the SS Friedrich Der Grosse

USS Huron (ID-1408)

USS Huron was a United States Navy transport ship during World War I. She was formerly the Norddeutscher Lloyd liner SS Friedrich der Grosse built in 1896, which sailed Atlantic routes from Germany and sometimes Italy to the United States and on the post run to Australia...

 a Norddeutscher Lloyd

Norddeutscher Lloyd

Norddeutsche Lloyd was a German shipping company. It was founded by Hermann Henrich Meier and Eduard Crüsemann in Bremen on February 20, 1857. It developed into one of the most important German shipping companies of the late 19th and early 20th centuries, and was instrumental in the economic...

 liner

Liner

Liner or LINER may refer to:In line drawing:* Eye liner, a type of makeup* Liner, a sable brush used by coach paintersIn linings:...

 that at the outset of World War I was interned by the United States in New York harbour. German sailors from the ship helped in manufacture. The SS Phoebus was chosen as a test case and as was reported in the Shipping News, "Accidents. S.S. Phoebus from New York—destination Archangel—caught fire at sea. Brought into port of Liverpool by H.M.S. Ajax

HMS Ajax (1912)

HMS Ajax was a King George V-class battleship , built at Scotts' shipyard at Greenock on the River Clyde...

."