Z-4190 bubble shield

The Bubble Shield, otherwise known as Shield Grenade, is a United Nations Space Command defensive device.

Mechanics
On top of the device is a safety cover, which can be flipped up to expose the red activation button. After that, it emits a charging sound and upon resting on the ground for a short time, creates the shield. The shield itself is a Buckminster Fuller sphere made of tessellating hexagons. Note that the bubble-"grenade" won't necessarily rest in place on the ground once activated. In the new Halo 3 ViDoc "Is Quisnam Protero Damno!" released by Bungie.net, the bubble-shield is seen used in the Alpha-stage Halo 3 footage for multiplayer. The bubble-grenade rolls down a hill as the Spartan-II concealed in the sphere back-peddals away from an enemy. Information later released by Bungie, though stated that the sphere would rest on the ground and the Spartan II would need to stand still to enjoy it's effects.

Appearances
It was first seen in the Halo 3 "Starry Night" CGI Trailer. Since Bungie stated that all assets in the commercial were produced by them, it is safe to say this device will show up in the game. Frankie has said that the shield is ONI tech.

It was seen again ingame in the Halo 3 ViDoc "Is Quisnam Protero Damno!". A player deployed it while running from BR fire. The shield successfully absorbed all projectiles and grenade explosions fired. It appears to be a large sphere-shaped object. It can roll around while activated. It appears uch larger than its first appearance in the Starry Night commercial.

This "object" is one of the few other deployable things, next to the Trip Mine and a Portable Grav Lift.

Differences
There is some shape difference in the Shield Bubble seen in the Starry Night trailer and the Halo 3 ViDoc. The deployable device in the Starry Night trailer was more cylidrical in shape and had a button on top. The deployable device in the Halo 3 ViDoc was more tire shaped (roundish) and had the button on it's circumfrence.

Tactics
The bubble shield projects a defensive field around the user when deployed that appears impervious to harm. In the latest ViDoc, it appears to be thrown onto the ground as a way of activation. It can create a forcefield and roll around to protect the user at the same time.

Speculation
When the staff of EGM magazine played a Halo 3 multiplayer beta, they mentioned that the "x" button had no function. One of the Bungie staff asked to another, "How many times did you press X?" and the other answered "Like 40 times, I wish this was activated." Maybe the shield is enabled by the X button.

It is speculated that with the introduction of the Spartan Laser which is a super weapon by definition, the gameplay may be one sided in multiplayer, so a super defensive option was introduced to balance the gameplay.

Frankie stated that the shield grenade is not necessarily a grenade. This could mean that you can activate it, pick it up again, wait for it to recharge and use it again. It also might have a time limit or a specific amount of damage it can take before it deactivates. It could also simply be a one-handed weapon with one use.

Considering humanity's current level of technology, it seems quite possible that as with the MJOLNIR shield system, this was created by reverse-engineering Covenant shield technology. It has been confirmed, however, that the shield grenade is human technology.

The aesthetics of the bubble-shield have changed somewhat from its first appearance, becoming larger and roughly spherical in shape. This may be due to the fact that what we've seen thus far is a very rough build. Frankie explained via weekly update that everything is much further along then what we got to see in the Vidoc.

Trivia

 * It has to be picked up, like the Trip Mine and Jump pad.