  The well studied blazar 3C 279 underwent a giant $\gamma$-ray outburst in
2014 March-April. The measured $\gamma$-ray flux (1.21 $\pm$ 0.10 $\times$
10$^{-5}$ ph cm$^{-2}$ s$^{-1}$ in 0.1-300 GeV energy range) is the highest
detected from 3C 279 by Fermi Large Area Telescope. Hour scale $\gamma$-ray
flux variability are observed, with a flux doubling time as short as 1.19 $\pm$
0.36 hours detected during one flare. The $\gamma$-ray spectrum is found to be
curved at peak of the flare suggesting low probability of detecting very high
energy (VHE; E $>$ 100 GeV) emission, which is further confirmed by the Very
Energetic Radiation Imaging Telescope Array System observations. The
$\gamma$-ray flux increased by more than an order in comparison to low activity
state and the flare consists of multiple sub-structures having fast rise and
slow decay profile. The flux enhancement is seen in all the wavebands though at
a lesser extent compared to $\gamma$-rays. During the flare, a considerable
amount of the kinetic jet power gets converted to $\gamma$-rays and the jet
becomes radiatively efficient. A one zone leptonic emission model is used to
reproduce the flare and we find increase in the bulk Lorentz factor as a major
cause of the outburst. From the observed fast variability, lack of VHE
detection, and the curved $\gamma$-ray spectrum, we conclude that the location
of the emission region cannot be far out from the broad line region (BLR) and
contributions from both BLR and torus photons are required to explain the
observed $\gamma$-ray spectrum.
