Throughout the three year run of Lost in Space weapons were regularly seen been carried or used by the crew of the Jupiter 2. These ranged from decidedly low tech knives through lasers to improvised weapons of great destructive force. In addition to offensive weapons, the Jupiter 2 campsite was protected by a forcefield generator which sat outside the space ship whenever the ship and its crew were on a planet for an extended length of time.
Major West is seen carrying a hunting knife in a sheath hung from his belt in the episodes “The Challenge” and “Magic Mirror,” although it is never seen in use as a weapon or as a tool. Reference is made to Will’s Swiss army knife in “The Raft” and “Follow the Leader.” The knife, famous for its multiple attachments, proved very useful in the former episode (but not as a weapon). Dr. Smith is also seen to carry a pocket knife in “There Were Giants in the Earth,” which he uses to slit open a gigantic mutant pea pod.
Two versions of the laser pistol appeared during the series’ run. In the first season the laser pistol was a rebuild of a space gun toy produced by Remco. This version is seen once or twice after the first season, but from season two on, it is replaced by a sleeker, silver pistol. The pistols are powerful weapons, capable of cutting through stone walls (see “The Hungry Sea”), but was completely ineffective against wide range of aliens encountered by the Robinsons (Raddion in “The Dream Monster” for example). Despite this, a single short blast was capable of killing one of the giant cyclopses in “There Were Giants in the Earth.”
Like the pistols, laser rifles came in two versions. The first version is black, like the early laser pistol, but a new silver version appeared after season one. There were actually three slightly different models of the newer rifles. The only difference between two of the newer ones was in the colour of the hand grip and butt; the third was of a completely different design and was the most commonly seen. Unlike the other two rifles, it had a large disk surrounding the barrel toward the end. As with the laser pistols, the rifles were not always effective against some of the creatures encountered by the Robinsons.
In “Deadliest of the Species” John and Don are able to jury rig a destructive field out of parts of their ship’s drive (fortuitously removed to the area in front of the Jupiter 2 for repairs). The female robot which has seduced the Robinson’s Robot is lured into the field where she is destroyed. Surprisingly, the destruction is not as complete as one first assumes, as the Robot is able to repair her afterwards, reforming her diabolical character.
The forcefield generator is frequently seen as set dressing in most on-planet episodes. It is frequently (it seems almost as a matter of routine) used at night, as well as when there is a more immediate threat. There are several aliens capable of passing through the field with little or no effect, but otherwise it seems to be the strongest of defences.
There is some contradiction in the actual function of the forcefield. In some episodes it is explicitly stated that one can safely pass through it away from the ship, but not reenter. In others, when its use is being tested, a rock thrown from the vicinity of the Jupiter 2 is destroyed as it passes out through the field. In addition, it is not clear whether the generator provides a “dome” of force around the ship automatically or whether the field must by “constructed” by panning the generator back and forth; on some occasions the generator is simply turned on, but at other times, it is moved about as if "building" a field of force where it is pointed.