Modern Use: While Molotov cocktails may be a psychologically effective method of disabling armoured fighting vehicles by forcing the crew out or damaging external components, most modern tanks cannot be physically destroyed or rendered completely inoperable by Molotov cocktails; only "disabled". Early Soviet tanks had poorly designed engine louvers which allowed the admission of fuel this design fault was quickly rectified, and subsequent armoured vehicles had engine louvers which drained fuel (as well as rain water and dust) away from the engine. Most tanks and infantry fighting vehicles (IFVs) of the 21st century have specially designed nuclear, biological and chemical protective systems that make them internally air-tight and sealed; they are well protected from vapors, gases, and liquids. Modern tanks possess very thick composite armour consisting of layers of steel, ceramics, plastics and Kevlar, and these materials have melting points well above the burning temperature of gasoline, which makes the vehicles themselves invulnerable to Molotov cocktails. Only external components such as optical systems, antennas, externally mounted weapons systems or ventilation ports and openings can be damaged, which can make a tank virtually "blind" or allow burning gasoline to seep into the vehicle, forcing the crew to at least open the hatches or perhaps abandon the vehicle. A Molotov cocktail thrown through an open hatch into the crew spaces would, like most other grenades, adversely and seriously affect the crew and equipment. However, many modern tanks (such as those operated by the US and NATO) have on-board fire suppression systems. Any fire in a crew space will be automatically extinguished with Halon or another fire suppressant. During the Second Battle of Fallujah US Marines employed Molotov cocktails made with "one part liquid laundry detergent, two parts gas" for 'burning out' their enemies from houses. In Northern Ireland, Molotov cocktails were used by rioting paramilitary groups and protesters against the police, and they are also used to attack houses to burn the house or to intimidate the occupants. In the Arab Spring, including in Cairo, Egypt, pro-government forces attacked protesters in Cairo with Molotovs. In the Bahraini uprising, protesters used Molotov cocktails against security forces. Legality: As incendiary devices, Molotov cocktails are illegal to manufacture or possess in many regions. In the United States, Molotov cocktails are considered "destructive devices" under the National Firearms Act and regulated by the ATF