Jump Jets
Jump Jets, often abbreviated to "JJ", enable a Mech or Battle Armor to become airborne briefly. They may only be fired for a limited time (indicated above the speed gauge in Mechs, and next to a Battle Armor's armor/health status)and require time to recharge. They also generate significant heat. Overheating will cause the JJs and weapons to be locked out.
The Final Beta 0.7.0 release introduced a new kind of JJ, called improved Jump Jets, or iJJ
Mechs
Generally, Jump Jets provide Mechs with several additional tactical options:
 Accessing terrain features too steep to climb.
 Quickly jumping to cover behind low hills.
 Briefly rising from behind cover to scout and assess the battlefield.
 Jump Sniping (aka Poptarting) from behind cover to fire weapons.
 Avoiding  to an extent  incoming missile fire.
By pressing [w] for forward, [s] for backward, [a] for left, and [d] for right, or by tilting the 'mech's torso by pitching up to go backwards and pitching down to go forwards, 'mechs can control the direction or "vector" of their jump (see adjacent Shadow Cat diagram). Standard jump jets have little to no ability to utilize right and left movement and only moderate control of forward and backward. For better control, some 'mechs have Improved Jump Jets.
Fluttering
Fluttering (pressing [Space] intermittently) can be used to maintain elevation during a jump to help with lock on weapons and help weapons with quick reload times take additional shots. Fluttering can also help prevent tripping and bouncing when jumping over a cliff edge, to do so, press [Space] long enough to clear the cliff edge, then press [Space+W] to vector forward onto the cliff.
Due to the way jump jets work in MechWarrior: Living Legends, expect assault and heavy mechs to jump much shorter distances than lighter mechs.
Improved Jump Jets
Improved Jump Jets (iJJ) are heavier than standard JJs and lose some of their vertical thrust for better vectoring (Using [WASD]), horizontal acceleration, and much better control over fuel consumption. Particularly advantageous is the ability to vector sideways rather than only forwards and backwards. This greatly increases a mech's evasive capabilities, like jumping to cover or dodging missiles. Improved Jump Jets, which take up twice the mass and space of standard jump jets, but produce less heat and allow for more nozzles to be fitted for a given engine allowing for a longer maximum jump distance.
A video showing the differences between both kinds can be found here: Jump Jets Preview
Note:
The heat generated by the use of either type of Jump Jets needs to be carefully considered in the overall management of a Mech's heat. For example, firing energy weapons midjump could result in a serious heat spike which could damage your Mech.
Battle Armor
Jump Jets are a key Battle Armor defense and method of locomotion. Jump Jets accelerate Battle Armors faster and further than 'Mechs and are substantially faster than sprinting with [shift]. This agility can make a skilled Battle Armour more difficult to hit, although it does reveal their position with a small plume of smoke.
Canon
Developed by the Terran Hegemony in 2471, thirty years after the introduction of the first BattleMech, the Mackie, and first appearing on the Wasp, Jump jets allow 'Mechs to navigate difficult terrain by rocketing over obstacles. Since their invention, jump jets have been adapted for use on other units. By harnessing the power of a 'Mech's fusion engine to superheat air or another suitable fluid, Jump Jets allow a BattleMech to briefly overcome gravity and rocket short distances over the battlefield.
BattleTech reference Jump_Jets
A modern refinement upon the centuries old design of standard jump jets, improved jump jets are twice as large and as heavy as their normal counterparts, but can propel a 'Mech further with less heat buildup.
BattleTech reference Improved_Jump_Jet
Usage
The following assets equip with Jump Jets or Improved Jump Jets :
Asset  Type  Faction  Tons  JJ  iJJ 

Commando Prime  Mech  IS  25  X  
Commando A  Mech  IS  25  X  
Commando B  Mech  IS  25  X  
Commando D  Mech  IS  25  X  
Commando E  Mech  IS  25  X  
Commando F  Mech  IS  25  X  
Locust IIC Prime  Mech  CL  25  X  
Locust IIC A  Mech  CL  25  X  
Locust IIC C  Mech  CL  25  X  
Locust IIC D  Mech  CL  25  X  
Locust IIC F  Mech  CL  25  X  
Locust IIC G  Mech  CL  25  X  
Solitaire A  Mech  CL  25  X  
Solitaire B  Mech  CL  25  X  
Solitaire E  Mech  CL  25  X  
Anubis Prime  Mech  IS  30  X  
Anubis C  Mech  IS  30  X  
Anubis E  Mech  IS  30  X  
Anubis G  Mech  IS  30  X  
Osiris Prime  Mech  IS  30  X  
Osiris B  Mech  IS  30  X  
Osiris C  Mech  IS  30  X  
Osiris E  Mech  IS  30  X  
Osiris F  Mech  IS  30  X  
Osiris G  Mech  IS  30  X  
Cougar A  Mech  CL  35  X  
Cougar B  Mech  CL  35  X  
Cougar C  Mech  CL  35  X  
Cougar E  Mech  CL  35  X  
Cougar F  Mech  CL  35  X  
Cougar G  Mech  CL  35  X  
Chimera Prime  Mech  IS  40  X  
Chimera B  Mech  IS  40  X  
Chimera C  Mech  IS  40  X  
Chimera E  Mech  IS  40  X  
Chimera F  Mech  IS  40  X  
HollanderII Prime  Mech  IS  45  X  
HollanderII B  Mech  IS  45  X  
HollanderII C  Mech  IS  45  X  
HollanderII D  Mech  IS  45  X  
HollanderII E  Mech  IS  45  X  
HollanderII F  Mech  IS  45  X  
HollanderII G  Mech  IS  45  X  
Shadowcat Prime  Mech  CL  45  X  
Shadowcat A  Mech  CL  45  X  
Shadowcat B  Mech  CL  45  X  
Shadowcat C  Mech  CL  45  X  
Shadowcat D  Mech  CL  45  X  
Shadowcat E  Mech  CL  45  X  
Shadowcat F  Mech  CL  45  X  
Shadowcat G  Mech  CL  45  X  
Hellhound Prime  Mech  CL  50  X  
Hellhound B  Mech  CL  50  X  
Hellhound D  Mech  CL  50  X  
Hellhound E  Mech  CL  50  X  
Hellhound F  Mech  CL  50  X  
Uziel Prime  Mech  IS  50  X  
Uziel A  Mech  IS  50  X  
Uziel B  Mech  IS  50  X  
Uziel C  Mech  IS  50  X  
Uziel D  Mech  IS  50  X  
Uziel F  Mech  IS  50  X  
Catapult Prime  Mech  IS  65  X  
Catapult A  Mech  IS  65  X  
Catapult B  Mech  IS  65  X  
Catapult C  Mech  IS  65  X  
Catapult D  Mech  IS  65  X  
Catapult E  Mech  IS  65  X  
Catapult F  Mech  IS  65  X  
Catapult G  Mech  IS  65  X  
Avatar A  Mech  IS  70  X  
Avatar B  Mech  IS  70  X  
Avatar D  Mech  IS  70  X  
Thor Prime  Mech  CL  70  X  
Thor A  Mech  CL  70  X  
Thor B  Mech  CL  70  X  
Thor C  Mech  CL  70  X  
Thor D  Mech  CL  70  X  
Thor E  Mech  CL  70  X  
Thor F  Mech  CL  70  X  
Thor G  Mech  CL  70  X  
Thanatos Prime  Mech  IS  75  X  
Thanatos A  Mech  IS  75  X  
Thanatos B  Mech  IS  75  X  
Thanatos C  Mech  IS  75  X  
Thanatos E  Mech  IS  75  X  
Thanatos G  Mech  IS  75  X  
MadCatMKII Prime  Mech  CL  90  X  
MadCatMKII A  Mech  CL  90  X  
MadCatMKII B  Mech  CL  90  X  
MadCatMKII C  Mech  CL  90  X  
MadCatMKII D  Mech  CL  90  X  
MadCatMKII F  Mech  CL  90  X  
MadCatMKII G  Mech  CL  90  X  
Sunder Prime  Mech  IS  90  X  
Sunder A  Mech  IS  90  X  
Sunder B  Mech  IS  90  X  
Sunder C  Mech  IS  90  X  
Sunder D  Mech  IS  90  X  
Sunder E  Mech  IS  90  X  
Sunder F  Mech  IS  90  X  
Sunder G  Mech  IS  90  X  
Archangel Prime  Mech  IS  100  X  
Archangel A  Mech  IS  100  X  
Archangel B  Mech  IS  100  X  
Archangel C  Mech  IS  100  X  
Archangel D  Mech  IS  100  X  
Archangel E  Mech  IS  100  X  
Kodiak Prime  Mech  CL  100  X  
Kodiak A  Mech  CL  100  X  
Kodiak B  Mech  CL  100  X  
Kodiak C  Mech  CL  100  X  
Kodiak D  Mech  CL  100  X  
Kodiak F  Mech  CL  100  X  
Kodiak G  Mech  CL  100  X 
All stats are current as of release 0.14.10  
